cc/gcc: build core compilers for canadian

Currently, we rely on an existing external cross-compiler targetting
the target, to build the C library.

This can pause quite a few problems if that compiler is different from
the one we are building, because it could introduce some ABI issues.

This patch removes this dependency, by building the core compilers
as we do for standard cross, and also by building the binutils and
gcc, for running on the build machine.

This means we no longer need to offer the cross-sompiler selection in
the menuconfig.

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

 # Bare metal config options

 ## select BARE_METAL

 ##

 ## help 'Bare metal' refers to those programs that run without any kernel.

 ## help

 ## help You probably want to say 'y' here if you plan to use your compiler

 ## help to build bootloaders. It is not yet suitable to build Linux kernels,

 ## help though, because the APCI stuff relies on the target C library headers

 ## help being available?!?!...