[PATCH] Build fix for lib/Support/Path.cpp

[Rafael Espíndola]

> I test the same patchsets on less-than-ancient darwin as well, and it causes
> no breakage on modern OS X.
> Dave's patch is functionally the same as what I have, so LGTM.
>
> I just have a comment in my patch that says where those defines are expected
> on darwin:
> // macros expected in <unistd.h>

OK. I don't think Dave has commit access. Can you commit his patch + comment?

Cheers,
Rafael