portlist, version: update build tags for Go 1.16, Apple M1

Build tags have been updated to build native Apple M1 binaries, existing build
tags for ios have been changed from darwin,arm64 to ios,arm64.

With this change, running go build cmd/tailscale{,d}/tailscale{,d}.go on an Apple
machine with the new processor works and resulting binaries show the expected
architecture, e.g. tailscale: Mach-O 64-bit executable arm64.

Tested using go version go1.16beta1 darwin/arm64.

Updates #943

Signed-off-by: moncho <50428+moncho@users.noreply.github.com>

portlist/netstat.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !darwin !arm64
+// +build go1.16,!ios !go1.16,!darwin !go1.16,!arm64
 
 package portlist
 

portlist/netstat_exec.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build windows freebsd openbsd darwin,amd64
+// +build windows freebsd openbsd darwin,amd64 go1.16,darwin,arm64
 
 package portlist
 

portlist/portlist_ios.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin,!amd64
+// +build go1.16,ios !go1.16,darwin,!amd64
 
 package portlist
 

portlist/portlist_macos.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin,amd64
+// +build darwin,amd64 go1.16,darwin,arm64
 
 package portlist
 

version/cmdname.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !darwin !arm64
+// +build go1.16,!ios !go1.16,!darwin !go1.16,!arm64
 
 package version
 

version/cmdname_ios.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin,arm64
+// +build go1.16,ios !go1.16,darwin,arm64
 
 package version