[llvm] r219189 - Support: Don't call close again if we get EINTR

[Rafael Espíndola]

> Most Unix-like operating systems guarantee that the file descriptor is
> closed after a call to close(2), even if close comes back with EINTR.
> For these systems, calling close _again_ will either do nothing or close
> some other file descriptor open(2)'d by another thread. (Linux)

Should we add an ifdef to avoid the sigmask dance on linux (and *BSD?)?

Cheers,
Rafael