In python shlib probe, cater for OpenBSD, which omits the .so symlink.

Most Unix-oid platforms provide a symlink "libfoo.so" -> "libfoo.so.n.n"
to allow the linker to resolve a reference "-lfoo" to a version-numbered
shared library.  OpenBSD has apparently hacked ld(1) to do this internally,
because there are no such symlinks to be found in their library
directories.  Tweak the new code in PGAC_CHECK_PYTHON_EMBED_SETUP to cope.
Per buildfarm member curculio.