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/Lex/PPMacroExpansion.cpp b/lib/Lex/PPMacroExpansion.cpp
index 9f962b0..6baa593 100644
--- a/lib/Lex/PPMacroExpansion.cpp
+++ b/lib/Lex/PPMacroExpansion.cpp
@@ -1290,7 +1290,8 @@
       LexUnexpandedToken(Tok);
       std::string WarningName;
       SourceLocation StrStartLoc = Tok.getLocation();
-      if (!FinishLexStringLiteral(Tok, WarningName, /*MacroExpansion=*/false)) {
+      if (!FinishLexStringLiteral(Tok, WarningName, "'__has_warning'",
+                                  /*MacroExpansion=*/false)) {
         // Eat tokens until ')'.
         while (Tok.isNot(tok::r_paren)
                  && Tok.isNot(tok::eod)