Incorrect inherent method resolution with multiple impls

[jonas-schievink]

struct S<T>(T);

trait Tr {}

impl<T: Tr> S<T> {
    fn call(&self, arg: u8) {}
}

impl S<()> {
    fn call(&self) {}
}

fn main() {
    S(()).call();
}

This gets a false-positive mismatched-arg-count diagnostic, because we choose the first impl block (despite the missing (): Tr impl), while the second one is actually correct.

This causes issues when using wasmer or wasm3, since they expose function handles with impls like these.

[lowr]

This is another case of #5441. Closing as it's been fixed 😄