Merge to upstream r225300.

Change-Id: I2b23715db9ac129ff80aa78ad5824db0a4d6fbb3

test/std/strings/basic.string.literals/literal2.fail.cpp

@@ -0,0 +1,20 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#include <string>
+#include <cassert>
+
+int main()
+{
+#if _LIBCPP_STD_VER > 11 
+    std::string foo  =   ""s;  // should fail w/conversion operator not found
+#else
+#error
+#endif
+}