prefix = path_join(NULL, ccan_dir, "ccan");
prefix = path_rel(NULL, take(prefix), dir);
prefix = tal_strcat(NULL, take(prefix), ": ");
prefix = path_join(NULL, ccan_dir, "ccan");
prefix = path_rel(NULL, take(prefix), dir);
prefix = tal_strcat(NULL, take(prefix), ": ");