Enable LLVM_ENABLE_WARNINGS when building standalone out of tree

When built within the llvm runtimes directory, the runtimes
CMakeLists.txt adds the same.

Differential Revision: https://reviews.llvm.org/D56981

llvm-svn: 351875
GitOrigin-RevId: 495c3d3c90d308fe700daad319fb49ce23180a52
1 file changed