exit(), panic if code >= 2**31

## code
`exit(2**31)`

## result
```thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /rustc/412f43ac5b4ae8c3599e71c6972112e9be4758fa/src/libcore/macros/mod.rs:15:40```

## expected result
in cpython if exit code overflow fallback to 0