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>

# Menu for the native GDB

config GDB_NATIVE

    bool

    prompt "Native gdb"

    depends on ! BARE_METAL

    depends on ! BACKEND

    help

      Build and install a native gdb for the target, to run on the target.

if GDB_NATIVE

config GDB_NATIVE_STATIC

    bool

    prompt "Build a static native gdb"

    help

      In case you have trouble with dynamic loading of shared libraries,

      you will find that a static gdb comes in handy.

endif # GDB_NATIVE