Don't dump llvm-config --cmakedir output if command fails.

This patch adjusts the out-of-tree CMake configuration so that
the stderr output is ignored when an old llvm-config is found
that doesn't support --cmakedir.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@291993 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed