systemd: make gcrypt optional

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

@@ -213,6 +213,7 @@ stdenv.mkDerivation {
     # while we do not run tests we should also not build them. Removes about 600 targets
     "-Dtests=false"
     "-Danalyze=${lib.boolToString withAnalyze}"
+    "-Dgcrypt=${lib.boolToString (libgcrypt != null)}"
     "-Dimportd=${lib.boolToString withImportd}"
     "-Dlz4=${lib.boolToString withCompression}"
     "-Dhomed=false"

pkgs/top-level/all-packages.nix

@@ -18676,6 +18676,7 @@ in
     withResolved = false;
     withTimedated = false;
     glib = null;
+    libgcrypt = null;
     lvm2 = null;
   };