message: enable a test that waited for a rustc fix
diff: // except according to those terms.
  // FIXME: remove -Zmir-opt-level once https://github.com/rust-lang/rust/issues/43359 is fixed
  -// FIXME: remove -Zmir-emit-validate=0 once https://github.com/rust-lang/rust/pull/43748 is merged
  -// compile-flags: -Zmir-opt-level=0 -Zmir-emit-validate=0
  +// compile-flags: -Zmir-opt-level=0
  use std::i32;
  