Implement P0403R1 - 'Literal suffixes for basic_string_view'. Requires clang 4.0 (specifically, r290744)

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@291457 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/string.view/string_view.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.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11
+// UNSUPPORTED: clang-3.3, clang-3.4, clang-3.5, clang-3.6, clang-3.7, clang-3.8, clang-3.9
+
+#include <string_view>
+#include <cassert>
+
+int main()
+{
+    std::string_view foo  =   ""sv;  // should fail w/conversion operator not found
+}