Non-local returns are not implemented

``` scala
object NonLocalReturn {
 def foo(a: List[Int]): Int = {
   a.foreach(x => return x)
   0
  }
}
```

Return will reach backend as part of 

``` scala
    private def $anonfun$foo$1(x: Int): Nothing = return x
```

triggering an error: 

```
assertion failed: Expected primitive types I - Lscala/runtime/Nothing$;
```
