Failures running rustc suite should fail nightly

[celinval]

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