Do you actually need a compiler that runs on those exotic systems, or just one that targets them? Because Rust (thanks to LLVM) is a whole lot better at the lat

Do you actually need a compiler that runs on those exotic systems, or just one that targets them? Because Rust (thanks to LLVM) is a whole lot better at the latter than the former, and it might well be possible to build something for your obscure UNIX. But for various reasons, Rust is not great at all at cross-compiling itself, so you would likely have to use something more conventional as your build server.