codegen.c: avoid integer comparison of different sign.
@@ -600,7 +600,7 @@ new_litbn(codegen_scope *s, const char *p, int base, mrb_bool neg)
codegen_error(s, "integer too big");
}
for (i=0; i<s->irep->plen; i++) {
- mrb_int len;
+ size_t len;
pv = &s->pool[i];
if (pv->tt != IREP_TT_BIGINT) continue;
len = pv->u.str[0];
