[CMake] [Darwin] Bug 21562 - Add a CMake equivalent for...

[CMake] [Darwin] Bug 21562 - Add a CMake equivalent for make/platform/clang_darwin.mk in compiler_rt

Summary: First pass at adding cc_kext_* builtin libraries. I need to cleanup and refactor the builtin filtering so that I can use it to filter the builtin symbols list, but this is the first step in the right direction.

Reviewers: bob.wilson, bogner, samsonov

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13115

llvm-svn: 248443