Fix freopen() where the path is null.

This has been in the standard since C99, but we've never supported it
before. It's apparently used by SPIRV-Tools.

I tried implementing this the other way (with fcntl(2)) first, but
eventually realized that that's more complicated and gives worse
results. This implementation assumes that /proc is mounted, but so much
of libc relies on that at this point that I don't think there's any
realistic case where the fcntl(2) implementation would be preferable,
and there are many where it's not.

The fact that no-one's mentioned this until now suggests that it's not a
heavily used feature anyway.

I've also replaced AssertCloseOnExec() with a CloseOnExec()
boolean-valued function instead, because it's really annoying getting
assertion failures that don't point you at the test line in question,
and instead point to some common helper code.

Test: treehugger
Change-Id: Ia2e53bf2664a4f782581042054ecd492830e2aed

0 files changed, 0 insertions, 0 deletions