Remove the old, and non-functional CMake build system from CompilerRT.

Remove the old, and non-functional CMake build system from CompilerRT.
I cannot build any part of this successfully on either Linux or Darwin,
and the replacement is worlds simpler by requiring that this be built as
a subproject of LLVM. If this breaks you for any reason, please let me
know, and let me know what your use case is.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@154059 91177308-0d34-0410-b5e6-96231b3b80d8