ices/78456.rs: fixed with errors

[github-actions]

Issue: rust-lang/rust#78456

#![feature(type_alias_impl_trait)]
#![no_std]

pub trait Tr<'x> {
    type Fut: core::future::Future<Output = ()>;

    fn f() -> Self::Fut;
}

impl<'x> Tr<'x> for () {
    type Fut = impl core::future::Future<Output = ()>;

    fn f() -> Self::Fut {
        async {
            //if false {
            return ();
            //}
            let res: Undef = ();
            res
        }
    }
}

=== stdout ===
=== stderr ===
error[E0412]: cannot find type `Undef` in this scope
  --> /home/runner/work/glacier/glacier/ices/78456.rs:18:22
   |
18 |             let res: Undef = ();
   |                      ^^^^^ not found in this scope

error[E0601]: `main` function not found in crate `78456`
  --> /home/runner/work/glacier/glacier/ices/78456.rs:1:1
   |
1  | / #![feature(type_alias_impl_trait)]
2  | | #![no_std]
3  | |
4  | | pub trait Tr<'x> {
...  |
21 | |     }
22 | | }
   | |_^ consider adding a `main` function to `/home/runner/work/glacier/glacier/ices/78456.rs`

error: language item required, but not found: `eh_personality`

error: `#[panic_handler]` function required, but not found

warning: unreachable statement
  --> /home/runner/work/glacier/glacier/ices/78456.rs:18:13
   |
16 |             return ();
   |             --------- any code following this expression is unreachable
17 |             //}
18 |             let res: Undef = ();
   |             ^^^^^^^^^^^^^^^^^^^^ unreachable statement
   |
   = note: `#[warn(unreachable_code)]` on by default

error: aborting due to 4 previous errors; 1 warning emitted

Some errors have detailed explanations: E0412, E0601.
For more information about an error, try `rustc --explain E0412`.
==============

[JohnTitor]

Indeed this was duplicate of rust-lang/rust#77993.