gnulib: fix stat/fstat build errors on old Windows version or using old MinGW

gnulib: fix stat/fstat build errors on old Windows version or using old MinGW

This commit imports two commits from gnulib's master branch fixing
a build error when building on a version of Windows that's older
than Vista, or when using an mingw's MinGW.

gnulib/ChangeLog:

	GDB PR build/26607
	* patches/0002-stat-fstat-windows-older-vista: New patch.
	* patches/0003-stat-fstat-windows-old-mingw: New patch.
	* update-gnulib.sh: Update to use the two new patches above.
	* import/m4/fstat.m4: Update after applying patches above.
	* import/m4/stat.m4: Ditto.
	* import/stat-w32.c: Ditto.
	* config.in: Regenerate.
	* configure: Regenerate.