[wwwdocs] Document some more libstdc++ additions in gcc-15

[Jonathan Wakely]

---

Changes for https://gcc.gnu.org/gcc-15/changes.html#libstdcxx

Are we missing anything else significant?

 htdocs/gcc-15/changes.html | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/htdocs/gcc-15/changes.html b/htdocs/gcc-15/changes.html
index c80ecc50..b23c7e74 100644
--- a/htdocs/gcc-15/changes.html
+++ b/htdocs/gcc-15/changes.html
@@ -426,7 +426,14 @@ asm (".text; %cc0: mov %cc2, %%r0; .previous;"
   </li>
   <li>Improved experimental support for C++26, including:
     <ul>
-    <li><code>views::concat</code>.</li>
+    <li><code>views::concat</code>, <code>views::to_input</code>,
+    <code>views::cache_latest</code>.
+    </li>
+    <li>
+      <code>&lt;stdbit.h&gt;</code> and <code>&lt;stdckdint.h&gt;</code>
+      headers.
+    </li>
+    <li><code>std::is_virtual_base_of<code> type trait.</li>
     <li>Member <code>visit</code>.</li>
     <li>Type-checking <code>std::format</code> args.</li>
     </ul>
-- 
2.49.0