Make issues similar to PR c++/68948 fail loudly.

	* semantics.c (finish_expr_stmt): If expr is error_mark_node,
	make sure we've seen_error().

From-SVN: r233183

gcc/cp/ChangeLog

+2016-02-05  Jason Merrill  <jason@redhat.com>
+
+	PR c++/68948
+	* semantics.c (finish_expr_stmt): If expr is error_mark_node,
+	make sure we've seen_error().
+
 2016-02-05  Patrick Palka  <ppalka@gcc.gnu.org>
 
 	PR c++/68948

gcc/cp/semantics.c

@@ -673,6 +673,9 @@ finish_expr_stmt (tree expr)
 
   if (expr != NULL_TREE)
     {
+      /* If we ran into a problem, make sure we complained.  */
+      gcc_assert (expr != error_mark_node || seen_error ());
+
       if (!processing_template_decl)
 	{
 	  if (warn_sequence_point)