[PATCH][darwin] revert to .weak_definition on darwin<10

[David Fang]

Hi,
 	On darwin8 and 9, -no-integrated-as fails to assemble with the 
system assembler (Apple's GNU as, 1.38) on the .weak_def_can_be_hidden 
directive, which use to emit .weak_definition.

http://llvm.org/bugs/show_bug.cgi?id=18100

 	Attached is a patch that brings back the old behavior for 
darwin<10, which is applicable to both darwin8 and 9, PPC and X86. 
The more correct thing to do is to characterize the non-integrated 
assembler being used and decide behavior that way, but currently there's 
no good way to propagate that information at runtime, so the assumed 
OS/tool version pairing is the next best thing.

Would this be acceptable?

David

-- 
David Fang
http://www.csl.cornell.edu/~fang/