ion3: explicitly disable parallel builds

pkgs/applications/window-managers/ion-3/default.nix

@@ -13,6 +13,11 @@ stdenv.mkDerivation rec {
 
   buildFlags = [ "LUA_DIR=${lua}" "X11_PREFIX=/no-such-path" "PREFIX=\${out}" ];
 
+  # Build system is missing depends for autogenerated export headers:
+  #   luac -o mod_tiling.lc mod_tiling.lua
+  #   main.c:21:10: fatal error: exports.h: No such file or directory
+  enableParallelBuilding = false;
+
   installFlags = [ "PREFIX=\${out}" ];
 
   meta = with lib; {