I have sussexfully updated rust (and cargo) to 1.79 on my PowerPC MUSL machine running Void.
xbps-src makes cross-building software so easy, in absolute most cases you only have to specify the target architecture and here we go — although it fails to produce a working dynamically-linked Python for PowerPC, but it looks like a bug in libffi. In any case you only have to worry about platform-specific workarounds, most of other stuff is done for you — and it just works!