[Ada] Allow gnatmake to construct libraries on x86_64-apple-darwin

[Arnaud Charlet]

> Use of a library GPR (which works fine with i386-apple-darwin) fails with
> "libraries are not supported on this platform".
> This is because gnattools/configure uses the test
>   powerpc-*-darwin* | *86-*-darwin*)
>     TOOLS_TARGET_PAIRS="mlib-tgt-specific.adb<mlib-tgt-specific-darwin.adb"
>     ;;
> The top-level configure uses *-*-darwin*, this should too.
> 
> I've tested this patch on both x86_64-apple-darwin10.2.0 and
> i386-apple-darwin10.2.0.
> 
> 2010-01-09  Simon Wright <simon@pushface.org>
> 
> 	PR ada/42659
> 	* configure.ac: gnatmake can construct libraries in all native
> 	Darwin architectures.
> 	* configure: Regenerate.

Yes, this is OK.

Arno