Add support for native Linux arm64 builds on Cirrus CI

[Jackenmen]

Support for native Linux arm64 on Cirrus CI wasn't added in #1191 due to some blockers on Cirrus CI's side.

It is likely going to be easy to solve this issue once at least one of these gets resolved:

• Support GCP's new Arm architecture cirruslabs/cirrus-ci-docs#1027
  • this would allow running a custom arm64 VM rather than just a container which will enable us to use Cirrus CI's Docker Builder VM image for the build (this could maybe even support Windows arm64 if and when Microsoft starts supporting generic arm64 rather than just what they can support while they have an exclusivity deal with Qualcomm)
• Docker in Docker with additional_containers doesn't seem to work? cirruslabs/cirrus-ci-docs#1034
  • this would allow running Docker in Docker on Cirrus CI which would enable us to run Docker daemon in an additional container and use that to run manylinux images

Until then, it might be possible to resolve this in some different way (potential contenders including spinning up a docker daemon in some different way or using cibuildwheel's Podman support instead) but it would not be that easy so I don't think it's worth pursuing before then.