[libc++][NFC] Fix documentation for using the libstdc++ test config
diff --git a/libcxx/test/configs/stdlib-libstdc++.cfg.in b/libcxx/test/configs/stdlib-libstdc++.cfg.in
index b9672f0..3ff0c54 100644
--- a/libcxx/test/configs/stdlib-libstdc++.cfg.in
+++ b/libcxx/test/configs/stdlib-libstdc++.cfg.in
@@ -9,7 +9,8 @@
#
# $ ./libcxx/utils/libcxx-lit <BUILD> -sv libcxx/test/std --param libstdcxx_install_prefix=/opt/homebrew/Cellar/gcc/14.1.0_1 \
# --param libstdcxx_version=14 \
-# --param libstdcxx_triple=aarch64-apple-darwin22
+# --param libstdcxx_triple=aarch64-apple-darwin22 \
+# --param stdlib=libstdc++
#
lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')