This reverts commit r259862, and attempts to fix builder CMakeCaches.

Will try this again some other time...

Conflicts:

	CMakeLists.txt
	tools/driver/CMakeLists.txt

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@259872 91177308-0d34-0410-b5e6-96231b3b80d8