[wwwdocs] Document C++17 static_assert feature

[Jonathan Wakely]

Patch for the /projects/cxx1z.html page to document the unary
static_assert in C++17.

Committed to CVS.

Index: htdocs/projects/cxx1z.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/projects/cxx1z.html,v
retrieving revision 1.8
diff -u -r1.8 cxx1z.html
--- htdocs/projects/cxx1z.html	20 Oct 2015 02:50:54 -0000	1.8
+++ htdocs/projects/cxx1z.html	19 Jan 2016 16:11:28 -0000
@@ -86,6 +86,12 @@
       <td class="supported" align="center"> 6 </td>
       <td>__cpp_nontype_template_args &gt;= 201411 </td>
     </tr>
+    <tr>
+      <td> Extending static_assert </td>
+      <td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3928.html";>N3928</a> </td>
+      <td class="supported" align="center">6</td>
+      <td> __cpp_static_assert &gt;= 201411 </td>
+    </tr>
     <!--
     <tr>
       <td> </td>