Convert makefiles to build LLVM/compiler-rt with CMake

Author: brson

README.md

@@ -19,6 +19,7 @@ Read ["Installing Rust"] from [The Book].
    * `g++` 4.7 or later or `clang++` 3.x
    * `python` 2.7 (but not 3.x)
    * GNU `make` 3.81 or later
+   * `cmake` 2.8.8 or later
    * `curl`
    * `git`