[Patch/Ada] Restore build of libgnat for mingw32

[Arnaud Charlet]

> This fixes:
> 
> 2007-10-21  Danny Smith <dannysmith@users.sourceforge.net>
> 
> 	Makefile.in (LIBGNAT_TARGET_PAIRS) Add s-tasinf-mingw.adb,
> 	s-tasinf-mingw.ads, a-exetim-mingw.adb, a-exetim-mingw.ads
> 	for win32 targets.
> 	(EXTRA_GNATRTL_TASKING_OBJS): Add a-exetim.o for win32 targets.

Yes, this patch is OK, thanks.

Arno