Since quite a long time, Gentoo Linux has problems building a GCC Toolchain for the AVR microcontroller architecture. This is just a short summary, how to get your toolchain running under Gentoo:
1. Emerge Toolchain
USE="-openmp -sanitize -vtv" crossdev -t avr -s4 -S --without-headers
2. Somehow, ldscripts go to /usr/x86_64-pc-linux-gnu/avr/lib/ldscripts but are actually expected to be located at /usr/avr/lib/ldscripts. A symlink quick fixes this issue
ln -s /usr/x86_64-pc-linux-gnu/avr/lib/ldscripts /usr/avr/lib/ldscripts
3. Have fun with your working toolchain