Regression test for const promotion with Option<Ordering>
https://rust.godbolt.org/z/EjxqE8WcTFixesrust-lang/rust#139093
Add a regression test to ensure that comparing `Option<Ordering>` to
`Some(Ordering::Equal)` does not trigger unnecessary const promotion
in MIR.
Previously, inlined constants like `Some(Ordering::Equal)` would get
promoted, leading to more complex MIR and redundant LLVM IR checks.
This test verifies that both the direct form and the `let`-binding form
now generate equivalent, simplified MIR.
r? cjgillot
486fae11ca