world builds again; no need for NO_GCC47 anymore

[John Marino]

There was a bootstrapping issue with the new GCC 4.7 that caused a 
broken world build for the vast majority of users.  As of commit
http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/ce38cc158226ab53f412af0f540e6a2e9d53b70f 
(Wed, 3 Oct 2012 08:33:48 +0000 (10:33 +0200)) this problem was resolved.

If you had set NO_GCC47 in your make.conf to work around it previously 
you can remove that now.

John