He's probably referring to this fragment in setup.py:


        if platform == 'darwin':
            # This should work on any unixy platform ;-)
            # If the user has bothered specifying additional -I and -L flags
            # in OPT and LDFLAGS we might as well use them here.
            #   NOTE: using shlex.split would technically be more correct, but
            # also gives a bootstrap problem. Let's hope nobody uses directories
            # with whitespace in the name to store libraries.
            cflags, ldflags = sysconfig.get_config_vars(
                    'CFLAGS', 'LDFLAGS')
            for item in cflags.split():
                if item.startswith('-I'):
                    inc_dirs.append(item[2:])
            for item in ldflags.split():
                if item.startswith('-L'):
                    lib_dirs.append(item[2:])


The entire block was added when I worked on the Mac port with Jack Jansen.  It ensures that additional include and lib directories specified through the 'OPT' and 'LDFLAGS' shell variables get added to the search path used by distutils.

As the comment says this should be safe all unity platforms, not just OSX.  IIRC the platform test is there because we couldn't easily test on other platforms and didn't want to accidentally break stuff (this was before we had a good buildbot setup).