[Patch][4.5] backport darwin t-make fragment fixes to 4.5

[IainS]

On 8 Jun 2010, at 08:56, IainS wrote:
> 	 Backport from mainline:
> 	 2010-05-28 Iain Sandoe <iains@gcc.gnu.org>
> 	* config.gcc (*-*-darwin*): Adjust t-make fragments for Darwin.
>
> <160410-4-5-tmakefrags-diff.txt>

With Mike's approval, ci to the branch as r160481.