xlockmore: disable format hardening to fix build

build output was empty since hardening was enabled by default

pkgs/misc/screensavers/xlockmore/default.nix

@@ -30,6 +30,8 @@ stdenv.mkDerivation rec {
       configureFlags+=" --enable-appdefaultdir=$out/share/X11/app-defaults"
     '';
 
+  hardeningDisable = [ "format" ]; # no build output otherwise
+
   meta = with lib; {
     description = "Screen locker for the X Window System";
     homepage = http://sillycycle.com/xlockmore.html;