[Patch libjava, darwin unwind] Do not use _darwin10_Unwind_FindEnclosingFunction except on darwin >= 10

[Mike Stump]

On Aug 15, 2010, at 1:45 PM, IainS wrote:
> This function should not be susbstituted on darwin versions with a working _Unwind_FindEnclosingFunction.
> (darwin 10 == OSX 10.6 BTW).
> 
> OK for trunk & 4.5?

Ok.