nixos: check config.system.build.initXml with xmllint

nixos-modules/genode-core.nix

@@ -141,7 +141,7 @@ in {
       };
 
     system.build.initXml = pkgs.buildPackages.runCommand "init.xml" {
-      nativeBuildInputs = with pkgs.buildPackages; [ dhall xorg.lndir ];
+      nativeBuildInputs = with pkgs.buildPackages; [ dhall xorg.lndir libxml2 ];
       DHALL_GENODE = "${pkgs.genodePackages.dhallGenode}/binary.dhall";
       BOOT_CONFIG = config.genode.boot.configFile;
     } ''
@@ -150,6 +150,7 @@ in {
         ${pkgs.genodePackages.dhallGenode}/.cache \
         $XDG_CACHE_HOME
       dhall text <<< "(env:DHALL_GENODE).Init.render (env:BOOT_CONFIG).config" > $out
+      xmllint --noout $out
     '';
 
   };