re-add multi-arch targets

[sophiewigmore]

Summary

This was rolled back by jam. We should wait to merge this until update builder.toml can consider targets.

Use Cases

Checklist

• [X] I have viewed, signed, and submitted the Contributor License Agreement.
• [ ] I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• [ ] I have added an integration test, if necessary.
• [X] I have reviewed the styleguide for guidance on my code quality.
• [X] I'm happy with the commit history on this PR (I have rebased/squashed as needed).