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>

# Dummy config file to not use a C library *at all*

## depends on BARE_METAL

##

## help Do not use a C library.

## help

## help This is usefull if your project is self-contained, does not rely on

## help an external C library, and provides all the necessary bits.

## help

## help Most probably usefull to bootloaders, as they generally don't depend

## help on the C library.

## help

## help If unsure: do *not* choose that, and use another option in the choice.