Update C++ DR status page

Author: AaronBallman

clang/www/cxx_dr_status.html

@@ -4739,7 +4739,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://cplusplus.github.io/CWG/issues/787.html">787</a></td>
     <td>CD2</td>
     <td>Unnecessary lexical undefined behavior</td>
-    <td class="unknown" align="center">Unknown</td>
+    <td class="unreleased" align="center">Clang 21</td>
   </tr>
   <tr id="788">
     <td><a href="https://cplusplus.github.io/CWG/issues/788.html">788</a></td>