fn regexp_new(vm: &mut VM, _: Value, args: &Args2) -> VMResult {
    args.check_args_num(1)?;
    let mut arg0 = vm[0];
    let string = arg0.expect_string("1st arg")?;
    let val = Value::regexp_from(vm, string)?;
    Ok(val)
}
Regexp.new(string, option=nil, code=nil) -> Regexp
Regexp.compile(string, option=nil, code=nil) -> Regexp
https://docs.ruby-lang.org/ja/latest/method/Regexp/s/compile.html
ruruby/src/builtin/regexp.rs