[wwwdocs] Document some recent libstdc++ changes

[Jonathan Wakely]

Committed to CVS.



Index: htdocs/gcc-9/changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-9/changes.html,v
retrieving revision 1.8
diff -u -r1.8 changes.html
--- htdocs/gcc-9/changes.html	8 Jun 2018 15:28:59 -0000	1.8
+++ htdocs/gcc-9/changes.html	20 Jun 2018 16:15:05 -0000
@@ -57,7 +57,15 @@
   </ul></li>
 </ul>
 
-<!-- <h4 id="libstdcxx">Runtime Library (libstdc++)</h4> -->
+<h4 id="libstdcxx">Runtime Library (libstdc++)</h4>
+<ul>
+  <li>Improved experimental support for C++2a,
+      including <code>std::remove_cvref</code>
+      and the <code>&lt;version&gt;</code> header.</li>
+  <li>Support for opening file streams with wide character paths on Windows</li>
+  <li>Incomplete support for the C++17 Filesystem library and the Filesystem
+      TS on Windows.</li>
+</ul>
 
 <!-- <h3 id="fortran">Fortran</h3> -->