toolchain builds for CI

[Michael Davidsaver]

fyi. To support EPICS development/maintenance I've been providing pre-built
binaries of the RTEMS toolchain and kernel for use in our continuous
integration builds.  Originally travis-ci.org, and more recently, github actions.

https://github.com/mdavidsaver/rsb/releases

I mention this now as I've recently expanded to include RTEMS 5 builds for
a number of BSPs, with additions being possible.  So there is a greater
chance of being useful to others.

* beatnik
* gen68360
* mcp750
* mvme167
* mvme2100
* mvme3100
* pc686 (w/ libbsd)
* qoriq_e500 (w/ libbsd)
* uC5282
* xilinx_zynq_a9_qemu (w/ libbsd)

The RTEMS 4.9/4.10 builds are limited to pc386.

The 20210306 sets of binaries are built on Ubuntu 20.04 (aka "focal"),
and are meant to be unpacked into '/', and will appear as eg. '/opt/rtems/5'.
(again, this is intended for use in disposable CI builders environments)

eg.

> wget https://github.com/mdavidsaver/rsb/releases/download/5%2F20210306/pc686-rtems5.tar.xz
> sudo tar -C / -xmJ -f pc686-rtems5.tar.xz
> ls /opt/rtems/5/bin/i386-rtems5-gcc
> ls /opt/rtems/5/i386-rtems5/pc686/Makefile.inc