What's the ARM64 backend status?

I don't see it obviously from https://github.com/gambit/gambit/blob/4584611a38736ac7bbd49486a9058b5e5989c538/gsc/_arm.scm , https://github.com/gambit/gambit/blob/master/gsc/_t-cpu-backend-arm.scm or configure.

ARM64 = smartphone

(For my own clarity, the compressed instruction set called ARM Thumb is a 32bit architecture only thing, ref. https://stackoverflow.com/questions/46086329/can-i-use-thumb-instructions-in-an-arm64-binary .)

Thanks,
Adam