systemd: avoid rebuild from the parent commit for now

Otherwise we'd be delaying this staging-next cycle noticeably.

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

@@ -66,6 +66,9 @@ in stdenv.mkDerivation {
 
   postPatch = ''
     substituteInPlace src/basic/path-util.h --replace "@defaultPathNormal@" "${placeholder "out"}/bin/"
+  ''
+    # TODO: unconditionalize on the next rebuild
+  + stdenv.lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''
     substituteInPlace src/boot/efi/meson.build \
       --replace \
       "find_program('ld'" \