[wwwdocs] Document C++20 and C++23 library additions

[Jonathan Wakely via Gcc-patches]

Pushed to wwwdocs.


commit 9f6040a13e7c552a8c1c65352b702dc5d71b369e
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Feb 1 12:40:46 2022 +0000

    Document C++20 and C++23 library additions

diff --git a/htdocs/gcc-12/changes.html b/htdocs/gcc-12/changes.html
index c6baee75..2719b9d5 100644
--- a/htdocs/gcc-12/changes.html
+++ b/htdocs/gcc-12/changes.html
@@ -305,6 +305,8 @@ a work-in-progress.</p>
   <li><code>std::vector</code>, <code>std::basic_string</code>,
       <code>std::optional</code>, and <code>std::variant</code>
       can be used in <code>constexpr</code> functions.</li>
+  <li><code>std::make_shared</code> for arrays with default initialization,
+      and <code>std::atomic&lt;std::shared_ptr&lt;T&gt;&gt;</code>.</li>
   <li>Layout-compatibility and pointer-interconvertibility traits.</li>
   </ul>
 </li>
@@ -315,6 +317,10 @@ a work-in-progress.</p>
   <li><code>&lt;spanstream&gt;</code></li>
   <li><code>std::invoke_r</code></li>
   <li><code>std::basic_string::resize_and_overwrite</code></li>
+  <li><code>&lt;stacktrace&gt;</code>
+      (not built by default, requires linking to an extra library).</li>
+  <li><code>&lt;stdatomic.h&gt;</code></li>
+  <li><code>constexpr std::type_info::operator==</code></li>
   </ul>
 </li>
 </ul>