bug#12632: file permissions checking mishandled when setuid

[Paul Eggert]

On 10/15/2012 08:46 PM, Eli Zaretskii wrote:
>> why bother to make a special case for F_OK?
> Because it's more universally available

faccessat is just as available, on the platforms that
the (patched) Emacs will run on: it's available either
natively or via supplied emulation.

> I believe also more efficient.

I thought the point of Bug#12587 was that on Windows,
'stat' can be way slower than faccessat, so much
so that Emacs appears unresponsive.

'stat' is also slower than faccessat on Solaris,
though the performance difference is not as great
as it appears to be on Windows.  'stat' is faster
than faccessat on GNU/Linux, true, but the
performance difference isn't great enough to make
a special case just for that platform.