Rustup for unsupported target triple

I'm thinking of getting a Pinebook Pro and running Void Linux musl edition on it, but then my target triple will be aarch64-unknown-linux-musl, for which nothing but std is compiled. I'd like to be able to manage and update components without depending on an external machine, so I'm wondering if there's a way to get rustup to download and compile from source, and then maybe bootstrap with an externally compiled rustc. I know this is way out there, but it would be really cool if I could do this.

Pinebook's 4GB of RAM may not be enough to compile LLVM and Rust.

I've tried doing some development on RPi4, and it was super painful. I've had to limit compilation to a single thread to avoid running out of memory, and a single thread on a small CPU takes forever.