gitlab-ci: add gcc-multilib to the docker image

This is needed for defconfigs that use syslinux.

Fixes https://gitlab.com/buildroot.org/buildroot/builds/11701092

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
2 files changed