Fix obj-c++.dg/encode-10.mm with cxx_dialect == cxx11.

	* constexpr.c (potential_constant_expression_1) [AT_ENCODE_EXPR]:
	Return false.

From-SVN: r222841

gcc/cp/ChangeLog

 2015-05-05  Jason Merrill  <jason@redhat.com>
 
+	* constexpr.c (potential_constant_expression_1) [AT_ENCODE_EXPR]:
+	Return false.
+
 	* semantics.c (finish_call_expr): Check complain.
 
 	* decl2.c (reset_type_linkage_2): Update the DECL_NAME of a

gcc/cp/constexpr.c

@@ -4159,6 +4159,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
     case OBJ_TYPE_REF:
     case TRANSACTION_EXPR:
     case ASM_EXPR:
+    case AT_ENCODE_EXPR:
     fail:
       if (flags & tf_error)
         error ("expression %qE is not a constant-expression", t);