No error when exporting from global augmentations

If you export a binding from the global scope, you're supposed to get an error unless you create a local binding and export it with whatever name you want.

```ts
export { Math };
// ~~~~
// Cannot export 'Math'. Only local declarations can be exported from a module.
```

However, we have a hole and allow exports that originate from a global augmentation. The following file is permitted with no error:

```ts
declare global {
var XYZ: number;
}

export { XYZ };
```

[Playground Link](https://www.typescriptlang.org/play/?#code/CYUwxgNghgTiAEBzCB7ARlC8DeAoeB8AbrPABoCaAWgFzwB2ArgLZogwDcuAvrriAA8ADihgAXHOWrxuHIA)