Completely bootstrap Rust from source
@JeremyRand suggested we use mrustc to remove the dependency on pre-built Rust binaries.
I believe it's a good idea, but not ready, yet: mrustc can bootstrap rustc 1.54.0, but we are using 1.60.0 for 102.
We'd need to compile at least 2 or 3 intermediate version to get the version we want to use, so I think we should not pursue this option until upstream supports a version that can compile 1.60 (which we could help doing, if we'd really wanted to close this issue).
However, I think it is an idea worth following.