Made the "expected string literal" diagnostic more expressive

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168267 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/ParseDeclCXX.cpp b/lib/Parse/ParseDeclCXX.cpp
index 0d785af..b8ebd9b 100644
--- a/lib/Parse/ParseDeclCXX.cpp
+++ b/lib/Parse/ParseDeclCXX.cpp
@@ -637,7 +637,8 @@
     return 0;
 
   if (!isTokenStringLiteral()) {
-    Diag(Tok, diag::err_expected_string_literal);
+    Diag(Tok, diag::err_expected_string_literal)
+      << /*Source='static_assert'*/1;
     SkipMalformedDecl();
     return 0;
   }