arm64 support

[vielmetti]

As noted in bufbuild/protoc-gen-validate#75 (comment) , the operating system automatic selection system at

https://github.com/bazelbuild/rules_go/blob/master/go/private/sdk.bzl#L29-L38

misidentifies an linux_arm64 system as linux_amd64 (because there is no case that properly matches the uname -p call). As it is written in that mentioned issue by @akonradi:

The issue is that if repository_ctx.os.name is 'linux', there's no way to set the host as linux_arm64 - it defaults to linux_amd64. See
https://github.com/bazelbuild/rules_go/blob/3b103d6954cd4508e1f63c8e2ea57bda18d98bcf/go/private/sdk.bzl#L31-L37

[vielmetti]

The similar issue for ppc64le was resolved at #854 and #1186 with a note also of changes near https://github.com/bazelbuild/rules_go/blob/master/go/platform/list.bzl#L34

[jayconrod]

At the moment, I don't have an arm64 machine to develop or verify this. I'm happy to accept a PR though.

[vielmetti]

Thanks @jayconrod - @moderation is working on this at https://github.com/moderation/rules_go/commit/20b05a8b4a635dd5ad822c4b8f5bbbb4a448d877 and has a test environment of some sort set up.

I'm happy to provide short or long term access to arm64 hardware via the Works on Arm cluster, http://worksonarm.com/cluster or http://github.com/worksonarm/cluster/issues/new .

[vielmetti]

There are notes on a port of Bazel to arm64 here http://zhiyisun.github.io/2017/02/15/Running-Google-Machine-Learning-Library-Tensorflow-On-ARM-64-bit-Platform.html but unfortunately they were never upstreamed.