> old, arcane and unused?

But it is used by retrocomputing enthusiasts. Linux has been supported by them for the platforms they care. They gladly hold up the bar “now you have to support Linux yourself”, with C compilers already existing and being supported by someone else. With Rust becoming a build-time dependency, things suddenly turn into “you're not getting any Linux until you port rustc to your platform and then make sure it's working there at all times”.