>> arm-none-eabi-toolchain is conflicting with avr-toolchain since both are
>> setting the CROSS_* environment variables. See the output of `avr-gcc -E -v -` below.
>>
>> This should probably be considered a bug. But I have no idea how to fix
>> this. :-( What do you think?
>
> I agree. The problem I see here is the environment variable game we have here.
> One option is to create cross compilers with the include paths inserted on them instead of taking environment variables as a default.

Or, we could have separate environment variables CROSS_AVR_C_INCLUDE_PATH
and CROSS_ARM_C_INCLUDE_PATH. But that sounds like too many environment
variables! :-P

> If they had the correct directories in their default includepaths
> everything would work correctly.
>
> I never did this before but it should be possible, probably affecting
> cross-gcc's configure step.

Something like this is possible too.

> We can start by pushing it and then keep solving the conflict issue
> and the upgrades to gcc-9.

Agreed.

>> Also, our avr-gcc package should probably be updated to the latest
>> avr-gcc-9.
>
> Once the current fix is applied next fixes should be possible.
> Why wasn't the patch included in the project?

I don't know. I have asked Danny at bug 24416 to push the patch. Let's
wait for a response.

Once Danny's patch is pushed, I'll open a new bug reporting the arm avr
conflict.

Also, I'm closing this bug report now since this issue is handled by
24416.

Thanks! :-)