[IshKebab]

You don't. It currently requires `-Z build-std=std,panic_abort` and some nightly flags (e.g. `#![feature(restricted_std)]`) but you can build `std` programs on bare metal targets. I can't remember exactly what it does if you try to open files or start threads or whatever (probably panics?) but you can compile and run it. If you don't do any of those things it works fine.

Currently the `sys` crate implementation is hard-coded into the compiler but eventually you will be able to provide it without modifying the compiler so you can e.g. target a RTOS or whatever.

It looks like that work started really recently actually:

https://github.com/rust-lang/rust/commit/99128b7e45f8b95d962...