nixos: fix two pipefail problems

It failed since 3c6efec2c0, i.e. #4453.
Now it should "work" the same as before.

nixos/modules/services/hardware/udev.nix

@@ -31,6 +31,7 @@ let
     buildCommand = ''
       mkdir -p $out
       shopt -s nullglob
+      set +o pipefail
 
       # Set a reasonable $PATH for programs called by udev rules.
       echo 'ENV{PATH}="${udevPath}/bin:${udevPath}/sbin"' > $out/00-path.rules

nixos/modules/system/boot/stage-1.nix

@@ -34,6 +34,8 @@ let
       doublePatchelf = pkgs.stdenv.isArm;
     }
     ''
+      set +o pipefail
+
       mkdir -p $out/bin $out/lib
       ln -s $out/bin $out/sbin