[Patch, Ada, Darwin] Remove use of "flat_namespace" linker flag.

[Arnaud Charlet]

Iain,

> So is the following OK for trunk?
> (no Ada regressions on *-darwin9, x86_64-darwin10).
> 
> cheers
> Iain
> 
> ada:
> 
> 	* gcc-interface/Makefile.in (darwin): Do not issue the
> 	'-flat_namespace'  linker flag during Ada build.
> 	 * mlib-tgt-specific-darwin.adb: Remove 'flat_namespace' flag from
> 	the default shared library options.

After double checking on our various test suites, this change is OK,
thanks.

Arno