How to use rustc-dev with fenix?

I am attempting to package Kani, a model checker for Rust.

Unfortunately, I am stuck on it being unable to find compiler crates:

kani> error[E0463]: can't find crate for `rustc_abi`
kani>   --> kani-compiler/src/
kani>    |
kani> 16 | extern crate rustc_abi;
kani>    | ^^^^^^^^^^^^^^^^^^^^^^^ can't find crate
kani>    |
kani>    = help: maybe you need to install the missing components with: `rustup component add rust-src rustc-dev llvm-tools-preview`

When I use Rust from Nixpkgs, it appears to find the crates (or at least it does not complain about them) but it will fail to build, even with the RUSTC_BOOTSTRAP hack, because it requires features from nightly rustc.

This is my attempt so far:

cc @figsoda :slight_smile:

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