I finally managed to build an ArchLinux kernel that supports out-of-tree modules written in Rust. If you're interested in the whole journey there are also the following posts:
* https://blog.rnstlr.ch/building-an-out-of-tree-rust-kernel-m...
* https://blog.rnstlr.ch/building-an-out-of-tree-rust-kernel-m...