fcitx5: depend on wayland-scanner

Otherwise, wayland-scanner would be picked up from the wayland in
buildInputs, which isn't cross-friendly and will stop working when we
split wayland-scanner into a separate package.

pkgs/tools/inputmethods/fcitx5/default.nix

@@ -5,6 +5,7 @@
 , pkg-config
 , cmake
 , extra-cmake-modules
+, wayland-scanner
 , cairo
 , pango
 , expat
@@ -60,6 +61,7 @@ stdenv.mkDerivation rec {
     cmake
     extra-cmake-modules
     pkg-config
+    wayland-scanner
   ];
 
   buildInputs = [