Merge branch 'sh-update-gcc8-sles' into 'master'

Enable gcc8 for SLES 12p5

See merge request https://gitlab.com/gitlab-org/gitlab-omnibus-builder/-/merge_requests/366

Merged-by: Balasankar 'Balu' C <balasankar@gitlab.com>
Approved-by: Balasankar 'Balu' C <balasankar@gitlab.com>
Reviewed-by: Balasankar 'Balu' C <balasankar@gitlab.com>
Co-authored-by: Stan Hu <stanhu@gmail.com>