Change CMake file formatting

Removing unnecessary spaces. For CACHE variables, putting the description string
on its own line which mimics libcxx. There are no logic changes.

Differential Revision: http://reviews.llvm.org/D9945

llvm-svn: 238219
GitOrigin-RevId: fbb1514805f4dfad3d7a3214d5d2f8860eab2579