Build darwin.arm64 binaries

[ashmckenzie]

This PR adds support for building darwin.arm64 binaries.

Checklist

Not all of these might apply to your change but the more you are able to check the easier it will be to get your contribution merged.

• [ ] CI passes
• [x] Description of proposed change
• [-] Documentation (README, docs/, man pages) is updated
• [-] Existing issue is referenced if there is one
• [-] Unit tests for the proposed change

[ashmckenzie]

WDYT @mrtazz ? In a separate PR, it might also be good to include linux.arm64 too?

[ashmckenzie]

May I please have your thoughts on this @mrtazz ?