[middle-end, trivial?] Use error_operand_p in gimplify_expr

[Paolo Carlini]

Hi,

was working on a couple of bugs and noticed what looks like a case of 
error_operand_p with a redundant check that TREE_TYPE is non-null. 
Barring objections I'm going to commit the below.

Thanks, Paolo.

///////////////////////

2017-19-12  Paolo Carlini  <paolo.carl...@oracle.com>

        * gimplify.c (gimplify_expr): Use error_operand_p.
Index: gimplify.c
===================================================================
--- gimplify.c  (revision 255811)
+++ gimplify.c  (working copy)
@@ -11334,9 +11334,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gi
       save_expr = *expr_p;
 
       /* Die, die, die, my darling.  */
-      if (save_expr == error_mark_node
-         || (TREE_TYPE (save_expr)
-             && TREE_TYPE (save_expr) == error_mark_node))
+      if (error_operand_p (save_expr))
        {
          ret = GS_ERROR;
          break;