[compiler-rt] Fix a bug in the cmakelists file when CMAKE_CXX_FLAGS are empty

Right now, the regex expression will fail if the flags were not set. Instead, we should follow the pattern of other llvm projects and quote the expression, so that it can work even when the flags are not set.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D92586

GitOrigin-RevId: 1410b72be3211fa2a3dffcc06c5dc904ae4a6fb4
1 file changed