[wwwdocs] Document additional symbols in libstdc++exp.a for GCC 13.3

[wwwdocs] Document additional symbols in libstdc++exp.a for GCC 13.3

[Jonathan Wakely]

The first two paragraphs are cloned from existing text for other point
releases. The third paragraph documents a recent backport that should be
called out in the release notes.

Pushed to wwwdocs.

---
 htdocs/gcc-13/changes.html | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/htdocs/gcc-13/changes.html b/htdocs/gcc-13/changes.html
index b4b1a39a..6930bd58 100644
--- a/htdocs/gcc-13/changes.html
+++ b/htdocs/gcc-13/changes.html
@@ -858,6 +858,32 @@ known to be fixed in the 13.2 release. This list might not be
 complete (that is, it is possible that some PRs that have been fixed
 are not listed here).</p>
 
+<!-- .................................................................. -->
+<h2 id="13.3">GCC 13.3</h2>
+
+<p>Note: GCC 13.3 has not been released yet, so this section is a
+work-in-progress.</p>
+
+<p>This is the <a href="https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&amp;resolution=FIXED&amp;target_milestone=13.3">list
+of problem reports (PRs)</a> from GCC's bug tracking system that are
+known to be fixed in the 13.3 release. This list might not be
+complete (that is, it is possible that some PRs that have been fixed
+are not listed here).</p>
+
+<h3>Language Specific Changes</h3>
+
+<h3>C++</h3>
+<ul>
+  <li>
+    The <code>libstdc++exp.a</code> library now includes all the Filesystem TS
+    symbols from the <code>libstdc++fs.a</code> library,
+    and the experimental symbols for the C++23 <code>std::stacktrace</code>
+    class from the <code>libstdc++_libbacktrace.a</code> library.
+    This means that <code>-lstdc++exp</code> is the only library needed for
+    all experimental libstdc++ features.
+  </li>
+</ul>
+
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