fn cmp(vm: &mut VM, self_val: Value, args: &Args2) -> VMResult {
    args.check_args_num(1)?;
    if self_val.id() == vm[0].id() {
        return Ok(Value::fixnum(0));
    }
    let self_val = self_val.into_module();
    let other = match vm[0].if_mod_class() {
        Some(m) => m,
        None => return Ok(Value::nil()),
    };
    if other.include_module(self_val) {
        Ok(Value::fixnum(1))
    } else if self_val.include_module(other) {
        Ok(Value::fixnum(-1))
    } else {
        Ok(Value::nil())
    }
}
## instance method Module#<=>
- self <=> other -> Integer | nil

https://docs.ruby-lang.org/ja/latest/method/Module/i/=3c=3d=3e.html
ruruby/src/builtin/module.rs