IAR: Add support for AVR
successfully compiling a simple hello world main file using IAR and cmake. I do not have access to older IAR-AVR compilers so I don't know how they differ, and how that might affect things like default C/CXX standards
Unfortunately my actual work projects have a TON of very specific and strange command line options for linker and compiler, so I don't have time to try to test it on that. Next time I have a little time I would like to actually do a simple project and try loading it onto hardware.
Fixes: #18557 (closed)