Using enclosing function's type parameter in enum definition yields ICE instead of error

``` rust
fn f<T>() { enum E { V(T) } }
pub fn main() { f::<int>(); }
```

⇒ error: internal compiler error: fictitious type ty_param({idx: 0, def_id: {crate: 0, node: 1}}) in sizing_type_of()

``` rust
fn f<T>() { struct S(T); }
pub fn main() { f::<int>(); }
```

⇒ error: attempt to use a type argument out of scope
