Adapt TESTrun constants for older Perl. [skip ci]

Solaris 9 has Perl 5.6.1, which does not support constant declaration
using a hash reference:

$ make check
./tests/TESTrun
Constant name 'HASH(0x2d8f0)' has invalid characters at ./tests/TESTrun
line 24
BEGIN failed--compilation aborted at ./tests/TESTrun line 24.
*** Error code 255
make: Fatal error: Command failed for target `check'

Declare one constant at a time to work around that and get "make check"
to start running tests (18 of which fail, but that's another issue).

(cherry picked from commit 85a27898f6b43579a108d995a5efad341f404c75)