systemd: disable building tests

We are currently not running any tests but building them takes
signitifcant amounts of time since they account to about 40% of all the
compilation targets.

pkgs/os-specific/linux/systemd/default.nix

@@ -62,7 +62,8 @@ stdenv.mkDerivation rec {
     "-Dloadkeys-path=${kbd}/bin/loadkeys"
     "-Dsetfont-path=${kbd}/bin/setfont"
     "-Dtty-gid=3" # tty in NixOS has gid 3
-    # "-Dtests=" # TODO
+    # while we do not run tests we should also not build them. Removes about 600 targets
+    "-Dtests=false"
     "-Dlz4=true"
     "-Dhostnamed=true"
     "-Dnetworkd=true"