The method_missing removal condition in was wrong.
MODIFY
src/kernel.c
src/kernel.c
@@ -969,7 +969,7 @@ mrb_method_missing(mrb_state *mrb, mrb_sym name, mrb_value self, mrb_value args)
* r.xxiii #=> 23
* r.mm #=> 2000
*/
-#ifndef MRB_DEFAULT_METHOD_MISSING
+#ifdef MRB_DEFAULT_METHOD_MISSING
static mrb_value
mrb_obj_missing(mrb_state *mrb, mrb_value mod)
{
@@ -1216,7 +1216,7 @@ mrb_init_kernel(mrb_state *mrb)
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 */
mrb_define_method(mrb, krn, "local_variables", mrb_local_variables, MRB_ARGS_NONE()); /* 15.3.1.3.28 */
-#ifndef MRB_DEFAULT_METHOD_MISSING
+#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, "methods", mrb_obj_methods_m, MRB_ARGS_OPT(1)); /* 15.3.1.3.31 */

The method_missing removal condition in a76dc04a was wrong.