lxqt-admin: fix ability to set timezone

* The timezone database file was not searched for in the correct
  location, giving an empty timezone list. Patch in the correct path.

* The time utility believed it was built on a non-systemd-based distro,
  and so used an incorrect method to manipulate the timezone. Tell it
  that it should use systemd.

The timezone list, and using the list to set the timezone, now work
properly. Note that the taskbar clock will only update to the correct
timezone on the next minute.

Author: tpwrules

pkgs/desktops/lxqt/lxqt-admin/default.nix

@@ -11,6 +11,7 @@
   qtsvg,
   qttools,
   qtwayland,
+  tzdata,
   wrapQtAppsHook,
   gitUpdater,
 }:
@@ -42,12 +43,22 @@ stdenv.mkDerivation rec {
     qtwayland
   ];
 
+  cmakeFlags = [
+    # fake finding of libsystemd; used to check if we are a systemd-based
+    # distro rather than actually being linked to
+    "-DLIBSYSTEMD_FOUND=TRUE"
+  ];
+
   postPatch = ''
     for f in lxqt-admin-{time,user}/CMakeLists.txt; do
       substituteInPlace $f --replace-fail \
         "\''${POLKITQT-1_POLICY_FILES_INSTALL_DIR}" \
         "$out/share/polkit-1/actions"
     done
+
+    # patch timezone database file location
+    substituteInPlace lxqt-admin-time/timeadmindialog.cpp \
+      --replace-fail "/usr/share/zoneinfo/zone.tab" "${tzdata}/share/zoneinfo/zone.tab"
   '';
 
   passthru.updateScript = gitUpdater { };