Nightly build failures

The build is currently failing on nightly due to:

* [x] A broken compiletest-rs (Fix: https://github.com/laumann/compiletest-rs/pull/130) - need to wait for new release or use master
* [x] A rustc bug: https://github.com/rust-lang/rust/issues/55376
