From Chris Lattners resume(http://nondot.org/sabre/Resume.html):

"Apple shipped the Mac OS X 10.8 and iOS 6 releases, and they were built virtually entirely with Clang - llvm-gcc is obsolete."

Another interesting thing: "We invested major effort into compiler implementation and tuning for the custom Apple CPU design known as the "Apple A6". The exceptional CPU performance of the iPhone 5 was a result of a joint effort between the Apple silicon and LLVM teams."