Merge remote-tracking branch 'origin/swift-3.0-branch' into stable

* origin/swift-3.0-branch:
  All triples that are valid macOS triples should have a darwin feature.
diff --git a/test/lit.common.cfg b/test/lit.common.cfg
index 91fd1f2..6f145d4 100644
--- a/test/lit.common.cfg
+++ b/test/lit.common.cfg
@@ -72,6 +72,9 @@
 if platform.system() == 'Windows' and '-win' in config.target_triple:
   config.environment['LIB'] = os.environ['LIB']
 
+if lit.util.isMacOSTriple(config.target_triple):
+   config.available_features.add('darwin')
+
 # Use ugly construction to explicitly prohibit "clang", "clang++" etc.
 # in RUN lines.
 config.substitutions.append(