Build src/port/dirmod.c only on Windows.
Since commit
ba7c5975adea74c6f17bdb0e0427ad85962092a2, port/dirmod.c
has contained only Windows-specific functions. Most platforms don't
seem to mind uselessly building an empty file, but OS X for one issues
warnings. Hence, treat dirmod.c as a Windows-specific file selected
by configure rather than one that's always built. We can revert this
change if dirmod.c ever gains any non-Windows functionality again.
Back-patch to 9.4 where the mentioned commit appeared.
projects / postgresql / commit