[wwwdocs] document Xtensa backend changes for 4.3

[Bob Wilson <bwilson@tensilica.com>]

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I have updated the 4.3 release notes to mention the Xtensa backend's change from 
sjlj to DWARF unwinding, and while I was at it, I included a few other less 
significant changes.  I checked the revised file with the HTML validator.


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Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-4.3/changes.html,v
retrieving revision 1.82
diff -u -r1.82 changes.html
--- changes.html	2 Nov 2007 07:27:23 -0000	1.82
+++ changes.html	14 Nov 2007 01:23:55 -0000
@@ -745,6 +745,20 @@
         option and can be accessed using new built-in functions.</li>
   </ul>
 
+<h3>Xtensa</h3>
+  <ul>
+    <li>Stack unwinding for exception handling now uses by default a
+	specialized version of DWARF unwinding.  This is not
+	binary-compatible with the setjmp/longjmp (sjlj) unwinding used 
+	for Xtensa with previous versions of GCC.</li>
+    <li>For Xtensa processors that include the Conditional Store option,
+	the built-in functions for atomic memory access are now implemented
+	using <code>S32C1I</code> instructions.</li>
+    <li>If the Xtensa NSA option is available, GCC will use it to implement
+	the <code>__builtin_ctz</code> and <code>__builtin_clz</code>
+	functions.</li>
+  </ul>
+
 
 <h2>Documentation improvements</h2>