I would like to know this as well. I mostly work with Renesas RH850 cores and was interested to be able to compile rust for them, but there is no v850 backend, sadly. Was considering fiddling with it, but couldn't figure out how.

I also hate the proprietary compilers for this arch, since they are sooo slooow (maybe for good reason, but I have no comparison point) and their licensing method just annoys me.