Revert a76dc04a to resolve #4820

src/kernel.c

@@ -685,7 +685,6 @@ mrb_method_missing(mrb_state *mrb, mrb_sym name, mrb_value self, mrb_value args)
  *     r.xxiii   #=> 23
  *     r.mm      #=> 2000
  */
-#ifdef MRB_DEFAULT_METHOD_MISSING
 static mrb_value
 mrb_obj_missing(mrb_state *mrb, mrb_value mod)
 {
@@ -698,7 +697,6 @@ mrb_obj_missing(mrb_state *mrb, mrb_value mod)
   /* not reached */
   return mrb_nil_value();
 }
-#endif
 
 static inline mrb_bool
 basic_obj_respond_to(mrb_state *mrb, mrb_value obj, mrb_sym id, int pub)
@@ -791,9 +789,7 @@ mrb_init_kernel(mrb_state *mrb)
   mrb_define_method(mrb, krn, "is_a?",                      mrb_obj_is_kind_of_m,            MRB_ARGS_REQ(1));    /* 15.3.1.3.24 */
   mrb_define_method(mrb, krn, "iterator?",                  mrb_f_block_given_p_m,           MRB_ARGS_NONE());    /* 15.3.1.3.25 */
   mrb_define_method(mrb, krn, "kind_of?",                   mrb_obj_is_kind_of_m,            MRB_ARGS_REQ(1));    /* 15.3.1.3.26 */
-#ifdef MRB_DEFAULT_METHOD_MISSING
   mrb_define_method(mrb, krn, "method_missing",             mrb_obj_missing,                 MRB_ARGS_ANY());     /* 15.3.1.3.30 */
-#endif
   mrb_define_method(mrb, krn, "nil?",                       mrb_false,                       MRB_ARGS_NONE());    /* 15.3.1.3.32 */
   mrb_define_method(mrb, krn, "object_id",                  mrb_obj_id_m,                    MRB_ARGS_NONE());    /* 15.3.1.3.33 */
   mrb_define_method(mrb, krn, "raise",                      mrb_f_raise,                     MRB_ARGS_ANY());     /* 15.3.1.3.40 */