go spec: update section on Implementation Differences

R=rsc, r
CC=golang-dev
https://golang.org/cl/4977046

doc/go_spec.html

 <!-- title The Go Programming Language Specification -->
-<!-- subtitle Version of July 14, 2011 -->
+<!-- subtitle Version of August 31, 2011 -->
 
 <!--
 TODO
@@ -5265,8 +5265,7 @@ The following minimal alignment properties are guaranteed:
 <h2 id="Implementation_differences">Implementation differences - TODO</h2>
 <ul>
 	<li><code>len(a)</code> is only a constant if <code>a</code> is a (qualified) identifier denoting an array or pointer to an array.</li>
-	<li><code>nil</code> maps are not treated like empty maps.</li>
-	<li>Trying to send/receive from a <code>nil</code> channel causes a run-time panic.</li>
-	<li><code>unsafe.Alignof</code>, <code>unsafe.Offsetof</code>, and <code>unsafe.Sizeof</code> return an <code>int</code>.</li>
+	<li>In gccgo, <code>nil</code> maps are not treated like empty maps.</li>
+	<li>In gccgo, trying to send/receive from a <code>nil</code> channel causes a run-time panic.</li>
 </ul>
 </span>