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

[David Fang]

Done.  r201255

>> 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?

-- 
David Fang
http://www.csl.cornell.edu/~fang/