configure: use AC_COMPILE_IFELSE() and AC_LANG_SOURCE() for testing flags.

That lets us completely control the program that's compiled with the
compiler flag we're testing, so we can make it a minimal program that
uses only prototype declarations and that therefore won't generate
warnings with some -W flags, e.g. -Wold-style-definition, and thus won't
falsely report those flags as unsupported.

diff --git a/aclocal.m4 b/aclocal.m4
index f12438aea29c7e672fd02905e302578aa59d7e21..c34a16b91e7f345d5ba426cfaeeb8905a28cddf1 100644 (file)
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -232,40 +232,22 @@ AC_DEFUN(AC_LBL_CHECK_COMPILER_OPT,
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
-       #
-       AC_TRY_COMPILE(
-           [],
-           [],
+       AC_COMPILE_IFELSE(
+           [AC_LANG_SOURCE([[int main(void) { return 0; }]])],
            [
                AC_MSG_RESULT([yes])
                CFLAGS="$save_CFLAGS"

diff --git a/configure b/configure
index d52bcc0592cbf3e10668e4de6492c35801173af6..dfe570ae17635f37bce8272ae20c14b0c370caf3 100755 (executable)
--- a/configure
+++ b/configure
@@ -6721,47 +6721,23 @@ $as_echo_n "checking whether the compiler supports the -W option... " >&6; }
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -6797,47 +6773,23 @@ $as_echo_n "checking whether the compiler supports the -Wall option... " >&6; }
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -6873,47 +6825,23 @@ $as_echo_n "checking whether the compiler supports the -Wassign-enum option... "
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -6949,47 +6877,23 @@ $as_echo_n "checking whether the compiler supports the -Wcast-qual option... " >
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7025,47 +6929,23 @@ $as_echo_n "checking whether the compiler supports the -Wmissing-prototypes opti
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7101,47 +6981,23 @@ $as_echo_n "checking whether the compiler supports the -Wmissing-variable-declar
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7177,47 +7033,23 @@ $as_echo_n "checking whether the compiler supports the -Wold-style-definition op
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7253,47 +7085,23 @@ $as_echo_n "checking whether the compiler supports the -Wpedantic option... " >&
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7329,47 +7137,23 @@ $as_echo_n "checking whether the compiler supports the -Wpointer-arith option...
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7405,47 +7189,23 @@ $as_echo_n "checking whether the compiler supports the -Wpointer-sign option...
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7481,47 +7241,23 @@ $as_echo_n "checking whether the compiler supports the -Wshadow option... " >&6;
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7557,47 +7293,23 @@ $as_echo_n "checking whether the compiler supports the -Wsign-compare option...
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7633,47 +7345,23 @@ $as_echo_n "checking whether the compiler supports the -Wstrict-prototypes optio
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7709,47 +7397,23 @@ $as_echo_n "checking whether the compiler supports the -Wunreachable-code-return
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7785,47 +7449,23 @@ $as_echo_n "checking whether the compiler supports the -Wused-but-marked-unused
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
@@ -7861,47 +7501,23 @@ $as_echo_n "checking whether the compiler supports the -Wwrite-strings option...
        save_ac_c_werror_flag="$ac_c_werror_flag"
        ac_c_werror_flag=yes
        #
-       # XXX - with autoconf 2.69, at least, the test program that this
-       # tries to compile is:
+       # We use AC_LANG_SOURCE() so that we can control the complete
+       # content of the program being compiled.  We do not, for example,
+       # want the default "int main()" that AC_LANG_PROGRAM() generates,
+       # as it will generate a warning with -Wold-style-definition, meaning
+       # that we would treat it as not working, as the test will fail if
+       # *any* error output, including a warning due to the flag we're
+       # testing, is generated; see
        #
-       # int
-       # main ()
-       # {
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
+       #    https://www.postgresql.org/message-id/2192993.1591682589%40sss.pgh.pa.us
        #
-       #   ;
-       #   return 0;
-       # }
-       #
-       # Hopefully, neither the empty statement nor the old-style
-       # definition of main() will, with any command-line flag
-       # whatsoever with which we test, on any compiler we test,
-       # will produce any warnings whatsoever; if it does, the
-       # command-line flag with which we test will be treated as
-       # not being supported even if it is supported.
-       #
-       # Thanks, autoconf, for making it *so* difficult to generate
-       # an absolute minimum valid C-with-everything-prototyped
-       # program as a test program, such as
-       #
-       #       int main(void) { return 0; }.
-       #
-       # (with autoconf 2.69, at least, using AC_LANG_CONFTEST() with
-       # AC_LANG_SOURCE([<code>]) produces the same function boilerplate
-       # as AC_LANG_PROGRAM([],[<code>]), complete with the main()
-       # function wrapper, the extra semicolon, and the return 0;,
-       # raising the question of "why, then, do both AC_LANG_SOURCE()
-       # and AC_LANG_PROGRAM() exist?").
+       # This may, as per those two messages, be fixed in autoonf 2.70,
+       # but we only require 2.64 or newer for now.
        #
        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
-int
-main ()
-{
-
-  ;
-  return 0;
-}
+int main(void) { return 0; }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :