lxqt-admin: fix ability to set timezone (#401521)

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 { };