You could also have a look at Support Rust std lib on RTEMS.
The above mentioned documentation chapter “16. Rust” of the RTEMS User Manual currently shows how to build Rust Bare Metal (i.e. without std lib). When you get that working, it may be a good idea to also try getting the existing port of Rust with std lib for ARM running with RTEMS. The brief documentation is here: armv7-rtems-eabihf Rust target