Changed CGObjCMac.cpp to add the marker externally_initialized to...

Changed CGObjCMac.cpp to add the marker externally_initialized to SELECTOR_REFERENCES in both the fragile and non-fragile API.

This is to ensure that GlobalOpt in LLVM does not attempt to look through a
selector reference to a method var name at compile time.

I also added a test/updated old tests that need to recognize the new keyword.

rdar://12580965.

llvm-svn: 174461