cc/gcc: add build frontend

Bizarrely enough, the core gcc are not enough to be able to build a
canadian cross, and a real, full cross compiler is required so that
the canadian cross can be properly built... WTF?!? Sigh...

Add a build-frontend, as was done for the binutils and the complibs.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 reporter_name="Nye Liu"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00046.html"

 reporter_comment=""