[babel 8] Align cli flags handling between `node` and `babel-node`

Given this file:
```js
console.log(typeof gc, process.argv.slice(2));
```

1. `node demo.js --expose-gc` logs `undefined [ '--expose-gc' ]`
2. `node --expose-gc demo.js` logs `function []`
3. `babel-node demo.js --expose-gc` logs `function []`
4. `babel-node --expose-gc demo.js` logs `function []`

(3) should behave the same as (1)