xfce.xfce4-systemload-plugin: Enable optional features

https://gitlab.xfce.org/panel-plugins/xfce4-systemload-plugin/-/blob/xfce4-systemload-plugin-1.3.3/configure.ac#L57-L61

Author: bobby285271

pkgs/desktops/xfce/panel-plugins/xfce4-systemload-plugin/default.nix

@@ -5,7 +5,9 @@
   gettext,
   pkg-config,
   xfce4-panel,
+  libgtop,
   libxfce4ui,
+  upower,
   xfconf,
   gitUpdater,
 }:
@@ -28,7 +30,9 @@ stdenv.mkDerivation rec {
   ];
 
   buildInputs = [
+    libgtop
     libxfce4ui
+    upower
     xfce4-panel
     xfconf
   ];