Streamline multi-platform building
What does this MR do and why?
According to https://docs.docker.com/build/guide/multi-platform/#platform-build-arguments, the TARGETARCH variable is automatically available for use in your Dockerfile when performing cross-platform compilation with the --platform flag.
It seems we can always use buildx with cross-compilation now, so this MR simplifies the code by using TARGETARCH.
Checklist
-
(If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.
Edited by Rémy Coutable