A super trait has been added to an auto trait.
Erroneous code example:
```compile_fail,E0568
#![feature(optin_builtin_traits)]
auto trait Bound : Copy {} // error!
fn main() {}
```
Since an auto trait is implemented on all existing types, adding a super trait
would filter out a lot of those types. In the current example, almost none of
all the existing types could implement `Bound` because very few of them have the
`Copy` trait.
To fix this issue, just remove the super trait:
```
#![feature(optin_builtin_traits)]
auto trait Bound {} // ok!
fn main() {}
```