Change warning about incomplete parsing of C++ default arg to error and provide a test case; thanks Doug!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@110603 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/ParseCXXInlineMethods.cpp b/lib/Parse/ParseCXXInlineMethods.cpp
index 8496ddd..fbb8a73 100644
--- a/lib/Parse/ParseCXXInlineMethods.cpp
+++ b/lib/Parse/ParseCXXInlineMethods.cpp
@@ -145,12 +145,8 @@
         else {
           if (Tok.is(tok::cxx_defaultarg_end))
             ConsumeToken();
-          else {
-            // Warn that there are tokens from the default arg that we left
-            // unparsed. This actually indicates a bug in clang but we avoid
-            // asserting because we want the parser robust.
-            Diag(Tok.getLocation(), diag::warn_default_arg_unparsed);
-          }
+          else
+            Diag(Tok.getLocation(), diag::err_default_arg_unparsed);
           Actions.ActOnParamDefaultArgument(LM.DefaultArgs[I].Param, EqualLoc,
                                             move(DefArgResult));
         }