Re-apply "cmake: Make CMAKE_BUILD_TYPE check case-insensitive"

This re-applies r244516 (effectively reverting r244516) without losing
the check that caused failures for VS.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244643 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed