[wwwdocs,committed] Start documenting libstdc++ changes for GCC 17

[Jonathan Wakely]

---
 htdocs/gcc-17/changes.html | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/htdocs/gcc-17/changes.html b/htdocs/gcc-17/changes.html
index 94d9bb72..0452a7f1 100644
--- a/htdocs/gcc-17/changes.html
+++ b/htdocs/gcc-17/changes.html
@@ -75,8 +75,17 @@ a work-in-progress.</p>
 
 <!-- <h3 id="c-family">C family</h3> -->
 
-<!-- <h3 id="cxx">C++</h3> -->
-<!-- <h4 id="libstdcxx">Runtime Library (libstdc++)</h4> -->
+<h3 id="cxx">C++</h3>
+<h4 id="libstdcxx">Runtime Library (libstdc++)</h4>
+<ul>
+<li>Improved experimental C++26 support including:
+  <ul>
+  <li><code>std::format</code> in <code>constexpr</code> functions.</li>
+  </ul>
+</li>
+<li><code>std::filesystem</code> support for Windows symlinks,
+    thanks to Adam Wood.</li>
+</ul>
 
 <!-- <h3 id="d">D</h3> -->
 
-- 
2.54.0