all: gofmt with Go 1.17

This adds "//go:build" lines and tidies up existing "// +build" lines.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

util/deephash/mapiter.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 !tailscale_go
 // +build !tailscale_go
 
 package deephash

util/deephash/mapiter_future.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 tailscale_go
 // +build tailscale_go
 
 package deephash

util/endian/big.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 mips || mips64 || ppc64 || s390x
 // +build mips mips64 ppc64 s390x
 
 package endian

util/endian/little.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 386 || amd64 || arm || arm64 || mips64le || mipsle || ppc64le || riscv64 || wasm
 // +build 386 amd64 arm arm64 mips64le mipsle ppc64le riscv64 wasm
 
 package endian

util/groupmember/groupmember_cgo.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 cgo
 // +build cgo
 
 package groupmember

util/groupmember/groupmember_noimpl.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 !cgo && !linux && !darwin
 // +build !cgo,!linux,!darwin
 
 package groupmember

util/groupmember/groupmember_notcgo.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 !cgo && (linux || darwin)
 // +build !cgo
 // +build linux darwin
 

util/osshare/filesharingstatus_noop.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 !windows
 // +build !windows
 
 package osshare

util/osshare/filesharingstatus_windows.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 windows
 // +build windows
 
 package osshare

util/pidowner/pidowner_noimpl.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 !windows && !linux
 // +build !windows,!linux
 
 package pidowner

util/racebuild/off.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 !race
 // +build !race
 
 package racebuild

util/racebuild/on.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 race
 // +build race
 
 package racebuild

util/systemd/systemd_linux.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 linux
 // +build linux
 
 package systemd

util/systemd/systemd_nonlinux.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 !linux
 // +build !linux
 
 package systemd

util/winutil/winutil.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 windows
 // +build windows
 
 // Package winuntil contains misc Windows/win32 helper functions.

util/winutil/winutil_notwindows.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 !windows
 // +build !windows
 
 package winutil