all: go fmt ./...

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: I30822eb504168b037ed3ec0f7759da1f41251f52
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/294374
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>

example/basic/main.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build darwin || linux || windows
 // +build darwin linux windows
 
 // An app that draws a green triangle on a red background.

example/basic/main_x.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build !darwin && !linux && !windows
 // +build !darwin,!linux,!windows
 
 package main