Fix a Python3 compatibility error
Fix a Python3 compatibility error

  File "clang/test/lit.cfg.py", line 186, in <module>
    config.available_features.add('macos-sdk-' + macOSSDKVersion)
TypeError: must be str, not bytes

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@365832 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang