[libcxx-commits] [libcxx] [libc++][doc] Update the release notes for LLVM 18 (PR #78324)

[Louis Dionne via libcxx-commits]

================
@@ -35,9 +35,25 @@ see the `releases page <https://llvm.org/releases/>`_.
 What's New in Libc++ 18.0.0?
 ==============================
 
-- A new debug mode has been added, replacing the legacy debug mode that was
-  removed in the LLVM 17 release. See ``libcxx/docs/Hardening.rst`` for more
-  details.
+The main focus of the libc++ team has been to implement new C++20, C++23,
+and C++26 features.
+
+A new debug mode has been added, replacing the legacy debug mode that was
+removed in the LLVM 17 release. See :ref:`hardening-modes` for more details.
----------------
ldionne wrote:

CC @var-const 
```suggestion
New hardened modes for the library have been added, replacing the legacy debug mode that was
removed in the LLVM 17 release. Unlike the legacy debug mode, some of these hardening modes are
also intended to be used in production. See :ref:`hardening-modes` for more details.
```

https://github.com/llvm/llvm-project/pull/78324