libguestfs: inherit hydraPlatforms from appliance

pkgs/development/libraries/libguestfs/default.nix

@@ -89,5 +89,7 @@ stdenv.mkDerivation rec {
     homepage = "http://libguestfs.org/";
     maintainers = with maintainers; [offline];
     platforms = platforms.linux;
+    # this is to avoid "output size exceeded"
+    hydraPlatforms = if appliance != null then appliance.meta.hydraPlatforms else platforms.linux;
   };
 }