just build, do not bootstrap, when building this port. This speeds
up a full port/package test cycle by 31% on a 4-core system; a simple
build/install will benefit even more.
(This may impact compile time by this compiler a bit, depending on
how well the system compiler optimizes this codebase. And we only
should do this for stable, established versions of GCC.)
On the way, update to the 20121102 snapshot of GCC 4.6.4.
Feature safe: yes