[PATCH] [compiler-rt] Use @rpath as LC_ID_DYLIB for ASan dylib on OS X

[kledzik at apple.com]

I'm not a clang driver guy, but it would probably be cleaner to leave AddLinkRuntimeLib() as is, and instead add the CmdArgs.push_back()s inside the if (Sanitize.needsAsanRt()).

It looks like the clang driver will always add two rpath entries when building for ASan?  Is there anyway to suppress that if Xcode knows better? That is, Xcode knows a better location for the runtime lib?

http://reviews.llvm.org/D6018