Make all our package sources use Go 1.17 gofmt format
(adding //go:build lines).
Not strictly necessary but will avoid spurious changes
as files are edited.
Part of //go:build change (#41184).
See https://golang.org/design/draft-gobuild
Change-Id: I01667f826428426a39c84717d02efa25fa44553c
Reviewed-on: https://go-review.googlesource.com/c/sys/+/294490
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Russ Cox <rsc@golang.org>