bug#18280: chmod: race condition

[Paul Eggert]

Tobias Stoeckmann wrote:
> For me, it sounds like configure should run a functionality test, calling
> fchmodat with AT_SYMLINK_NOFOLLOW and see if it fails and ENOTSUP is set
> in errno.  In that case, don't call fchmodat or force 0 for flags,
> otherwise use AT_SYMLINK_NOFOLLOW.

Yes, that sounds like a reasonable way to move forward.  At least, that 
is what I was thinking of doing in 2012.  I never got around to it, 
partly because (although it's an improvement) it's not a complete fix 
for the race.