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

llvm-svn: 365832
diff --git a/clang/test/lit.cfg.py b/clang/test/lit.cfg.py
index 4fd8eb3..ca8a05d 100644
--- a/clang/test/lit.cfg.py
+++ b/clang/test/lit.cfg.py
@@ -183,7 +183,7 @@
 lit.util.usePlatformSdkOnDarwin(config, lit_config)
 macOSSDKVersion = lit.util.findPlatformSdkVersionOnMacOS(config, lit_config)
 if macOSSDKVersion is not None:
-    config.available_features.add('macos-sdk-' + macOSSDKVersion)
+    config.available_features.add('macos-sdk-' + str(macOSSDKVersion))
 
 if os.path.exists('/etc/gentoo-release'):
     config.available_features.add('gentoo')