Auto merge of #126139 - compiler-errors:specializes, r=lcnr

Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl

Fixes (after backport) rust-lang/rust#125197

### What

rust-lang/rust#122791 makes it so that inductive cycles are no longer hard errors. That means that when we are testing, for example, whether these impls overlap:

```rust
impl PartialEq<Self> for AnyId {
    fn eq(&self, _: &Self) -> bool {
        todo!()
    }
}

impl<T: Identifier> PartialEq<T> for AnyId {
    fn eq(&self, _: &T) -> bool {
        todo!()
    }
}
```

...given...

```rust
pub trait Identifier: Display + 'static {}

impl<T> Identifier for T where T: PartialEq + Display + 'static {}
```

Then we try to see if the second impl holds given `T = AnyId`. That requires `AnyId: Identifier`, which requires that `AnyId: PartialEq`, which is satisfied by these two impl candidates... The `PartialEq<T>` impl is a cycle, and we used to winnow it when we used to treat inductive cycles as errors.

However, now that we don't winnow it, this means that we *now* try calling `candidate_should_be_dropped_in_favor_of`, which tries to check whether one of the impls specializes the other: the `specializes` query. In that query, we currently bail early if the impl is local.

However, in a foreign crate, we try to compute if the two impls specialize each other by doing trait solving. This may itself lead to the same situation where we call `specializes`, which will lead to a query cycle.

### How does this fix the problem

We now record whether specialization is enabled in foreign crates, and extend this early-return behavior to foreign impls too. This means that we can only encounter these cycles if we truly have a specializing impl from a crate with specialization enabled.

-----

r? `@oli-obk` or `@lcnr`

Author: bors