Patch: cygwin fix

[Tom Tromey]

>>>>> "Anthony" == Anthony Green <green@redhat.com> writes:

Anthony> But it seems to me that cygwin is and should always be using posix.h. 
Anthony> Should I just move this to posix.h then?

Won't cygwin sometimes want some special handling?  It's been a long
time since I did any cygwin hacking...

I wonder why this problem doesn't affect mingw builds as well.

Yes, let's move this to posix.h.  Let's isolate the system-specific
clutter as much as we can...

Tom