[guix] Build for arm-linux-gnueabihf and aarch64-linux-gnu

Summary: Enable the build for ARM linux and AARCH64 on guix.

Test Plan:

HOSTS="arm-linux-gnueabihf aarch64-linux-gnu" contrib/guix/guix-build

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15457