cmd/lncli: add watchtower client commands

cmd/lncli/wtclient_default.go

@@ -0,0 +1,10 @@
+// +build !wtclientrpc
+
+package main
+
+import "github.com/urfave/cli"
+
+// wtclientCommands will return nil for non-wtclientrpc builds.
+func wtclientCommands() []cli.Command {
+	return nil
+}