swaylock: support cross-compilation

pkgs/applications/window-managers/sway/lock.nix

···
 { lib, stdenv, fetchFromGitHub
-, meson, ninja, pkg-config, scdoc
+, meson, ninja, pkg-config, scdoc, wayland-scanner
 , wayland, wayland-protocols, libxkbcommon, cairo, gdk-pixbuf, pam
 }:
 
···
       --replace "version: '1.4'" "version: '${version}'"
   '';
 
-  nativeBuildInputs = [ meson ninja pkg-config scdoc ];
+  nativeBuildInputs = [ meson ninja pkg-config scdoc wayland-scanner ];
   buildInputs = [ wayland wayland-protocols libxkbcommon cairo gdk-pixbuf pam ];
 
   mesonFlags = [