RSB Architecture request: aarch64, x86_64, risc-v

[Chris Johns]

Hello,

I would like to add aarch64, x86_64, and risc-v to 4.12/rtems-all so these tools
are always built when regression testing tool set changes. This change makes
sure the tools are in a suitable state for those looking to add support for
these architectures.

To add RISC-V I need the architecture added to the RSB. Could those working with
this architecture to please considering post patches to this list list for
review that adds this architecture.

Thanks
Chris