`core::hint::must_use` returns a temporary

Originally noticed in https://github.com/rust-lang/rust/issues/124478#issue-2267570324, @GKFX identified it as a problem in must_use in https://github.com/rust-lang/rust/issues/124478#issuecomment-2081492040

I tried this code:

#![feature(hint_must_use)]

fn foo() -> &'static [usize] {
    &[core::hint::must_use(42)]
}

I expected to see this happen: no error, the value is a constant

Instead, this happened:

error[E0515]: cannot return reference to temporary value
 --> src/lib.rs:4:5
  |
4 |     &[core::hint::must_use(42)]
  |     ^--------------------------
  |     ||
  |     |temporary value created here
  |     returns a reference to data owned by the current function

For more information about this error, try `rustc --explain E0515`.
error: could not compile `playground` (lib) due to 1 previous error

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rustc 1.79 nightly 2024-04-27

Start with the reproducer in src/lib.rs and the reported E0515 diagnostic, then trace how core::hint::must_use is handled in this expression. Done means the example no longer reports a reference to a temporary while preserving the intended constant behavior, with a regression test covering it.