checking for which compiler is in use

[Greg Troxel <gdt%lexort.com@localhost>]

I just fixed 5 instances of

  ${PKGSRC_COMPILER} == "gcc"

which fail when PKGSRC_COMPILER is "ccache gcc" or "distcc gcc", plus
one such test for clang.

This resolves a problem where openjade crashes when built under pkgsrc
with ccache, where a workaround was previously not applied.

I think all of my fixes are correct, but I'm sure someone will let me
know if not.

I believe pkgsrc is now free of this problem.