Add support for MacOS ARM64 (M1)

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[google-cla[bot]]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

:memo: Please visit https://cla.developers.google.com/ to sign.

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• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

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[mattoddie]

@googlebot I signed it!

[whesse]

These formulas are automatically modified by code in the bin and lib directories, so this code (maybe just the list of files, which currently doesn't include mac-arm) needs to be changed as well.

The ARM Mac SDK is still a preview, and should not be made the default download on M1 for homebrew until we move it out of preview, I believe. @mit-mit