[Bug target/92729] [avr] Convert the backend to MODE_CC so it can be kept in future releases

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92729

--- Comment #4 from Tobias Burnus <burnus at gcc dot gnu.org> ---
See also https://gcc.gnu.org/pipermail/gcc/2020-April/thread.html#402 (for
details/current status, ask those involved).