Rust uses LLVM, which likely should have easier time being ported than an entire Rust compiler. Rust handles cross-compilation pretty well so you don't have to compile on an actual embedded device, or something.

I wonder if an LLVM backend that issues a very simple and predictable subset of C would be a viable way to support exotic old architectures which only have a C compiler. LLVM-cbe is a thing: https://github.com/JuliaComputing/llvm-cbe