[CMake] Split -gx strip flag into -g -x

llvm-strip doesn't handle -gx spelling, so we need to split these
as two separate flags.

Differential Revision: https://reviews.llvm.org/D50684

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339639 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed