Go: don't use the sync/atomic package unless absolutely necessary

[kormat]

It turns out there's an alignment "bug" that triggers when you use sync/atomic on structures that aren't aligned according to the platform rules.

https://golang.org/pkg/sync/atomic/#pkg-note-BUG
golang/go#599

This causes subtle cross-platform bugs, and is not worth the complexity for non-critical paths.

[lukedirtwalker]

There is now a vet pass called atomicalign that should detect those issues. We should use that.
(see golang/go#11891 (comment))
(see https://godoc.org/golang.org/x/tools/go/analysis/passes/atomicalign)

[kormat]

@lukedirtwalker : In that case we'd want to have automated testing on at least arm, otherwise we won't know when it breaks.

[kormat]

Oh, even worse - bazel doesn't support arm as a host platform, so we can't actually build on an arm vm => can't do automated testing.

[scrye]

Closing as unactionable. However, note that we have 0 uses of sync/atomic in the code base at the moment, so it looks like this is already avoided by us never needing such low-level concurrency optimization primitives.