Failures running rustc suite should fail nightly #39
Description
We still have a few failures to fix until we enable this. Track issues that are blocking rustc suite. Once they have all been fixed, we can enable this:
### Tasks
- [ ] #38
- [ ] https://github.com/rust-lang/project-stable-mir/issues/40
- [ ] https://github.com/rust-lang/project-stable-mir/issues/41