[C++ PATCH] fix constrait diag

[Nathan Sidwell]

Changing '%qE %S' to '%<E %S%>' is missing a % and ICES constraints/req4.

Fixed thusly.
--
Nathan Sidwell

2017-05-04  Nathan Sidwell  <nat...@acm.org>

	* constraint.cc (diagnose_check_constraint): Fix %E thinko.

Index: constraint.cc
===================================================================
--- constraint.cc	(revision 247613)
+++ constraint.cc	(working copy)
@@ -2859,7 +2859,7 @@ diagnose_check_constraint (location_t lo
     {
       if (elide_constraint_failure_p ())
         return;
-      inform (loc, "in the expansion of concept %<E %S%>", check, sub);
+      inform (loc, "in the expansion of concept %<%E %S%>", check, sub);
       cur = get_concept_definition (decl);
       tsubst_expr (cur, targs, tf_warning_or_error, NULL_TREE, false);
       return;