build: add build tag noselfupdate

Allow downstream packaging to build rclone without selfupdate command:
$ go build -tags noselfupdate

Fixes #5187

cmd/selfupdate/help.go

@@ -1,3 +1,5 @@
+// +build !noselfupdate
+
 package selfupdate
 
 // Note: "|" will be replaced by backticks in the help string below

cmd/selfupdate/noselfupdate.go

@@ -0,0 +1,11 @@
+// +build noselfupdate
+
+package selfupdate
+
+import (
+	"github.com/rclone/rclone/lib/buildinfo"
+)
+
+func init() {
+	buildinfo.Tags = append(buildinfo.Tags, "noselfupdate")
+}

cmd/selfupdate/selfupdate.go

@@ -1,3 +1,5 @@
+// +build !noselfupdate
+
 package selfupdate
 
 import (

cmd/selfupdate/selfupdate_test.go

@@ -1,3 +1,5 @@
+// +build !noselfupdate
+
 package selfupdate
 
 import (

cmd/selfupdate/verify.go

@@ -1,3 +1,5 @@
+// +build !noselfupdate
+
 package selfupdate
 
 import (

cmd/selfupdate/writable_unix.go

@@ -1,4 +1,5 @@
 // +build !windows,!plan9,!js
+// +build !noselfupdate
 
 package selfupdate
 

cmd/selfupdate/writable_unsupported.go

@@ -1,4 +1,5 @@
 // +build plan9 js
+// +build !noselfupdate
 
 package selfupdate
 

cmd/selfupdate/writable_windows.go

@@ -1,4 +1,5 @@
 // +build windows
+// +build !noselfupdate
 
 package selfupdate