John Marino has added a ‘gcc47’ compiler ccvar, so you can build world and kernel with it.  ‘It’ is actually gcc-aux, since it seems to work better than the basic (“vanilla”?)  gcc47.  You also get Ada support, though that wasn’t the driving reason to pick it.  This is brand new so don’t try it unless you’re ready to discover issues.

Is there any other BSD able to use gcc 4.7 for world/kernel?  Even 4.6?  Most of the attention has been on clang.