> BTW, is there any resource point to why the package of the
> avr-toolchain 5.5 is broken?

I searched through my mail and I don't remember exactly where I read
that avr-toolchain 5.5 is broken and avr-toolchain 4.9 works. I was only
able to find this very old thread hinting about the problem.

https://lists.gnu.org/archive/html/guix-devel/2016-08/msg00667.html

Please feel free to open a new bug report.

> I may spend some time trying to make it work.

That would be great! :-) It's a pain to have a package so important as
avr-toolchain not working for so long. If it can't be fixed immediately,
I think we should temporarily remove it so as to not frustrate users who
would expect it to work normally.