Enable ovni for cross compilation

Reviewed-by: Aleix Boné <abonerib@bsc.es>
Tested-by: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

pkgs/ovni/default.nix

@@ -55,4 +55,7 @@ in
     doCheck = true;
     checkTarget = "test";
     hardeningDisable = [ "all" ];
+    meta = {
+      cross = true;
+    };
   }