Reduce garbage from push_to_top_level.

	* name-lookup.c (do_push_to_top_level): Don't allocate
	current_lang_base.
	(do_pop_from_top_level): Release current_lang_base.

From-SVN: r261860

gcc/cp/ChangeLog

 2018-06-21  Jason Merrill  <jason@redhat.com>
 
+	* name-lookup.c (do_push_to_top_level): Don't allocate
+	current_lang_base.
+	(do_pop_from_top_level): Release current_lang_base.
+
 	Let -fmem-report see callers of cxx_make_type.
 	* lex.c (cxx_make_type): Add MEM_STAT_DECL.
 	(make_class_type): Likewise.

gcc/cp/name-lookup.c

@@ -6852,7 +6852,7 @@ do_push_to_top_level (void)
 
   scope_chain = s;
   current_function_decl = NULL_TREE;
-  vec_alloc (current_lang_base, 10);
+  current_lang_base = NULL;
   current_lang_name = lang_name_cplusplus;
   current_namespace = global_namespace;
   push_class_stack ();
@@ -6872,7 +6872,7 @@ do_pop_from_top_level (void)
     invalidate_class_lookup_cache ();
   pop_class_stack ();
 
-  current_lang_base = 0;
+  release_tree_vector (current_lang_base);
 
   scope_chain = s->prev;
   FOR_EACH_VEC_SAFE_ELT (s->old_bindings, i, saved)