Use `mrb_open_core()` instead of `mrb_open()`  in `mrbc`
@@ -271,7 +271,7 @@ dump_file(mrb_state *mrb, FILE *wfp, const char *outfile, struct RProc *proc, st
int
main(int argc, char **argv)
{
- mrb_state *mrb = mrb_open();
+ mrb_state *mrb = mrb_open_core(NULL, NULL);
int n, result;
struct mrbc_args args;
FILE *wfp;
