replace mrb_iv_set by mrb_obj_iv_set

src/variable.c

@@ -747,13 +747,13 @@ mrb_vm_const_set(mrb_state *mrb, mrb_sym sym, mrb_value v)
   struct RClass *c = mrb->ci->proc->target_class;
 
   if (!c) c = mrb->ci->target_class;
-  mrb_iv_set(mrb, mrb_obj_value(c), sym, v);
+  mrb_obj_iv_set(mrb, (struct RObject*)c, sym, v);
 }
 
 void
 mrb_define_const(mrb_state *mrb, struct RClass *mod, const char *name, mrb_value v)
 {
-  mrb_iv_set(mrb, mrb_obj_value(mod), mrb_intern(mrb, name), v);
+  mrb_obj_iv_set(mrb, (struct RObject*)mod, mrb_intern(mrb, name), v);
 }
 
 void