IncorrectCguReuseType
In [100753], `IncorrectCguReuseType` accidentally stopped being emitted. Begin emitting it again rather than just blindly dropping it, and adjust tests accordingly. [100753]: https://github.com/rust-lang/rust/pull/100753/commits/706452eba74026c51e8d0fa30aee2497c69eafc0#diff-048389738ddcbe0f9765291a29db1fed9a5f03693d4781cfb5aaa97ffb3c7f84
CGU tests require CGU code to be exercised. We can't merely do "cargo check" on these tests.