Add colored diagnostics when building LLVM with cmake + ninja + clang

When invoked from Ninja, clang does not detect that it can use colors : see https://github.com/martine/ninja/issues/174

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182878 91177308-0d34-0410-b5e6-96231b3b80d8
Don't assume the registers will be enumerated sequentially.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182879 91177308-0d34-0410-b5e6-96231b3b80d8