[wwwdocs] Update gcc-9/changes.html

[Marek Polacek]

Applied.

Index: gcc-9/changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-9/changes.html,v
retrieving revision 1.47
diff -u -r1.47 changes.html
--- gcc-9/changes.html	28 Feb 2019 10:31:50 -0000	1.47
+++ gcc-9/changes.html	28 Feb 2019 20:51:01 -0000
@@ -187,6 +187,10 @@
       of <code>std::initializer_list</code> that are likely to result in a
       dangling pointer, such as returning or assigning from a temporary
       list. </li>
+    <li><a href="https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#index-Wredundant-move"><code>-Wredundant-move</code></a>, implied by <code>-Wextra</code>, warns about redundant calls to
+    <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>
   </ul></li>
 
   <li>