core: do not attempt to add 'private' symlinks when RootImage/RootDirectory are used

A bind mount is added directly from private on the host to the actual
destination directory, no need for the symlinks (which cannot be created
as the bind mount happens first and creates the target as an actual directory)

Fixes https://github.com/systemd/systemd/issues/22264

src/core/execute.c

@@ -3373,7 +3373,7 @@ static int compile_symlinks(
                                         return r;
                         }
 
-                        if (!exec_directory_is_private(context, dt))
+                        if (!exec_directory_is_private(context, dt) || exec_context_with_rootfs(context))
                                 continue;
 
                         private_path = path_join(params->prefix[dt], "private", context->directories[dt].items[i].path);