non-fatal overflow makes more code compile

[lcnr]

duh

e.g. during coherence: https://rust.godbolt.org/z/1PMobhaK7

trait Indirect<T> {}

impl<T: Overflow<()>> Indirect<T> for () {}

trait Overflow<U> {}
impl<T, U> Overflow<U> for Box<T>
where
    U: Indirect<Box<Box<T>>>,
{}

trait NotImplemented {}

trait Trait<U, DUMMY> {}
impl<T, U> Trait<U, u32> for T
where
    // T: NotImplemented, // causes old solver to succeed
    U: Indirect<T>,
    T: NotImplemented,
{}

impl<DUMMY> Trait<(), DUMMY> for Box<u32> {}

fn main() {}