[wwwdocs] Update gcc-9/changes.html #2

[Marek Polacek]

One more.

Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-9/changes.html,v
retrieving revision 1.48
diff -u -r1.48 changes.html
--- changes.html        28 Feb 2019 20:51:28 -0000      1.48
+++ changes.html        28 Feb 2019 21:48:53 -0000
@@ -191,6 +191,8 @@
     <code>std::move</code>.</li>
     <li><a 
href="https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#index-Wpessimizing-move";><code>-Wpessimizing-move</code></a>,
 implied by <code>-Wall</code>, warns when a call to
     <code>std::move</code> prevents copy elision.</li>
+    <li><a 
href="https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#index-Wclass-conversion";><code>-Wclass-conversion</code></a>,
 on by default, warns when a conversion function will never be
+    called due to the type it converts to.</li>
   </ul></li>
 
   <li>