nixos/systemd: fix make unit failed when unit too large

        { preferLocalBuild = true;

          allowSubstitutes = false;

          inherit (unit) text;

          passAsFile = [ "text" ];

        }

        ''

          name=${shellEscape name}

          mkdir -p "$out/$(dirname -- "$name")"

          echo -n "$text" > "$out/$name"

          mv "$textPath" "$out/$name"

        ''

    else

      pkgs.runCommand "unit-${mkPathSafeName name}-disabled"