Cmake changes

Rant: I'll send more details and a patch as soon as I have one, but I
must say - every time someone fiddles with the cmake in this project
it gets broken.

whoever pushed the broken cmake changes to the 37 release branch -
revert that shit please. I mentioned already that it's causing a
problem and should certainly *not* be merged to a release branch which
has already been tagged.

This goes against almost every llvm project standard practice if I'm
not mistaken.