ia32: Add keep edge to cached nodes

If the cached nodes like NoReg_GP, ... had no keep edge and no users
then irgwalks could miss them leading for the iredges code to miss
initializing these nodes.

This fixes bug 161.

ir/be/bespillutil.c

@@ -1076,6 +1076,9 @@ static bool has_real_user(const ir_node *node)
 
 static void add_missing_keep_walker(ir_node *node, void *data)
 {
+	if (!sched_is_scheduled(node))
+		return;
+
 	(void)data;
 	if (get_irn_mode(node) == mode_T) {
 		unsigned const n_outs = arch_get_irn_n_outs(node);

ir/be/ia32/bearch_ia32.c

@@ -80,6 +80,9 @@ static inline ir_node *create_const(ir_graph *irg, ir_node **place,
 	ir_node *res   = func(NULL, block);
 	arch_set_irn_register(res, reg);
 	*place = res;
+	/* We need a keep edge on our cached nodes, so that following firm
+	 * irgwalks will not miss them. */
+	keep_alive(res);
 	return res;
 }