all: add macOS ARM64 port

[cherrymui]

See discussion in #38485. Honestly I don't know why we need a separate issue from #38485. Maybe we just need one started with "proposal:"?

Maintainer: I guess I could be a maintainer for the time being...

[dmitshur]

Thanks for making this proposal. This corresponds to the following requirements in https://golang.org/wiki/PortingPolicy#requirements-for-a-new-port:

• A proposal must be filed and accepted in which the Go team accepts overall responsibility for having the new port in the core Go tree.

• At least one developer must be named (and agree) to maintain the port, by making required updates in a timely manner as architecture or operating system requirements change.

Also see #39782, which is the tracking issue for adding a builder for this port.

/cc @andybons @cagedmantis @toothrot FYI.

[rsc]

Given that we already have macOS and we have arm64 (and also all the Macs in the world will be arm64 before long, so the alternative is dropping the macOS port entirely), this seems fine and can be fast-tracked. This seems like a likely accept.

[rsc]

No change in consensus, so accepted.

[cherrymui]

Thanks.

[cherrymui]

As far as I can tell, the darwin/arm64 port is now pretty much on parity with the darwin/amd64 port (CLs are tracked under #38485), and I don't expect much more to be done on this issue. I think we can close this.

Feel free to reopen, or open a new issue, if I missed anything.

[domino14]

will it be available for download?

[dmitshur]

@domino14 Yes, that's the plan for Go 1.16. The tracking issue for that is #42756, please subscribe to it for updates.