[PATCH,AVR] Fix PR34879 Wrong code builtin setjmp nolocal_goto

[Andy H]

Thank you for review. I will correct format.

> Further changes may be required in the future if AVR 24bit jumps are to be
> supported.
>
> The avr6 architecture now included in avr back-end. This patch work 
> for 256K devices? Again, I against to add partially working feature.
>   

The OLD comment in bug report refers to YOUR changes to make avr6 work!
The patch corrects framepointer it does not change any code pointer, 
labels etc.
It does not depend on size of code pointers.

Andy