bug#28023: fix make-temp-file race on local host

[Paul Eggert]

On 08/09/2017 09:05 AM, Eli Zaretskii wrote:
> We could resolve this problem by providing a way for the Windows build
> to specify its own replacements for 'open', 'mkdir', and 'lstat'
> (Emacs already have such replacements in w32.c), which tempname.c
> calls, but that would require minor changes in Gnulib's tempname.c.

This sounds like a better way to go. What minor changes would be needed? 
tempname.c already includes config.h, which includes ms-w32.h, which 
redefines open, mkdir, and lstat, so I thought it would work as-is.

> This seems to say that we will sometimes use secure_getenv, but the
> relevant code in tempname.c is conditioned on _LIBC, which AFAIU is
> only true when building glibc, so why do we need that?  Or did I miss
> something?
No, good catch, Emacs never needs secure_getenv. I fixed Gnulib, 
installed the attached patch to propagate that fix, and will adjust the 
proposed make-temp-file patch accordingly.

0001-Merge-from-gnulib.patch
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