fstat: Fix time_t values on native Windows platforms.
* doc/posix-functions/fstat.texi: Mention the problem with st_*time.
* lib/stat-w32.h: New file.
* lib/stat-w32.c: New file.
* lib/fstat.c: Don't include msvc-inval.h. Include msvc-nothrow.h,
stat-w32.h instead.
(fstat_nothrow): Remove function.
(rpl_fstat): Implement by means of _gl_fstat_by_handle.
* m4/fstat.m4 (gl_FUNC_FSTAT): On native Windows, set REPLACE_FSTAT
always.
(gl_PREREQ_FSTAT): Require gl_HEADER_SYS_STAT_H.
* modules/fstat (Files): Add lib/stat-w32.h, lib/stat-w32.c.
(Depends-on): Remove msvc-inval. Add pathmax, msvc-nothrow.
(configure.ac): Also compile lib/stat-w32.c.