Add this to make.conf:
QEMU_SOFTMMU_TARGETS="arm"
QEMU_USER_TARGETS="arm"
Add this to package.use:
app-emulation/qemu static-user
emerge qemu --ask
Register ARM:
echo ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm:' > /proc/sys/fs/binfmt_misc/register
systemctl restart systemd-binfmt