[PATCH] If lld binary is named 'ld' on darwin, use darwin driver mode

[kledzik at apple.com]

Adding support for "ld" on *nix meaning use-gnu-driver is reasonable, but it is an additional feature (which I have no way to test).

What would be the correct way to test for that?  
   #if LLVM_ON_UNIX && !__APPLE_

http://reviews.llvm.org/D5282