[wwwdocs] Document std::is_scoped_enum support

[Jonathan Wakely via Gcc-patches]

Pushed to wwwdocs.

commit 3aca43b28c04f6d0c7f446bafcd2f539a2eec5b0
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Fri Mar 19 20:12:01 2021 +0000

    Document std::is_scoped_enum support

diff --git a/htdocs/gcc-11/changes.html b/htdocs/gcc-11/changes.html
index 9734eee8..99fb9d8f 100644
--- a/htdocs/gcc-11/changes.html
+++ b/htdocs/gcc-11/changes.html
@@ -483,7 +483,7 @@ a work-in-progress.</p>
       <li><code>contains</code> member functions for strings,
         thanks to Paul Fee.
       </li>
-      <li><code>std::to_underlying</code></li>
+      <li><code>std::to_underlying</code>, 
<code>std::is_scoped_enum</code></li>
     </ul>
   </li>
   <li>Experimental support for Data-Parallel Types (<code>simd</code>)