serve ftp: disable on plan9 since it doesn't compile

cmd/serve/ftp/ftp.go

@@ -1,3 +1,7 @@
+// Package ftp implements an FTP server for rclone
+
+//+build !plan9
+
 package ftp
 
 import (

cmd/serve/ftp/ftp_test.go

@@ -3,7 +3,7 @@
 //
 // We skip tests on platforms with troublesome character mappings
 
-//+build !windows,!darwin
+//+build !windows,!darwin,!plan9
 
 package ftp
 

cmd/serve/ftp/ftp_unsupported.go

@@ -0,0 +1,11 @@
+// Build  for unsupported platforms to stop go complaining
+// about "no buildable Go source files "
+
+// +build plan9
+
+package ftp
+
+import "github.com/spf13/cobra"
+
+// Command definition is nil to show not implemented
+var Command *cobra.Command = nil

cmd/serve/serve.go

@@ -15,7 +15,9 @@ func init() {
 	Command.AddCommand(http.Command)
 	Command.AddCommand(webdav.Command)
 	Command.AddCommand(restic.Command)
-	Command.AddCommand(ftp.Command)
+	if ftp.Command != nil {
+		Command.AddCommand(ftp.Command)
+	}
 	cmd.Root.AddCommand(Command)
 }