build/clang_darwin: Fix previous change to CheckArches to not cause problem when
command produces error output on stdout instead of stderr (and suppress the
stderr output while at it).

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@133019 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed