Fixed typo in wwwdocs

[Nicola Pero]

Committed as obvious.

Thanks

Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-4.6/changes.html,v
retrieving revision 1.70
diff -u -r1.70 changes.html
--- changes.html        22 Nov 2010 15:26:24 -0000      1.70
+++ changes.html        23 Nov 2010 18:38:32 -0000
@@ -483,7 +483,7 @@
     header file automatically selects the new API.  Support for the
     old API is being phased out and upgrading the software to use the
     new API is strongly recommended.  To check for the availability of
-    the new API, the <code>__GNU_LIBOBJC_</code> macro can be used as
+    the new API, the <code>__GNU_LIBOBJC__</code> macro can be used as
     older versions of the GNU Objective-C runtime library, which do
     not support the new API, do not define such a macro.</li>