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

[Rui Ueyama]

It's a small feature. You can write it and the buildbots will tell you you did it right :)

I'm not an expert of lit tests. I'd probably write it using shell and uname command with "REQUIRES: shell", but I'm not sure if it's the correct way.

http://reviews.llvm.org/D5282