Squelch a warning with Capsicum enabled. [skip appveyor]

Squelch a warning with Capsicum enabled. [skip appveyor]

The Capsicum workaround I added in commit 706c79e causes a side effect
on FreeBSD 11.4, 12.2 and 13.0 with local libpcap when Capsicum is
enabled, that is, in CMake builds (Capsicum detection is broken in
Autoconf builds, as it turns out).  Add a workaround for the side effect
as well and get rid of another warning and respective exemption:

tcpdump.c:2286:3: warning: implicit declaration of function 'bpf_dump'
  is invalid in C99 [-Wimplicit-function-declaration]

(cherry picked from commit 51f9c3b947eac89254c4e3662902487e0844a699)