cc/gcc: do not use the core pass-2 to build the baremetal compiler

In case we build a baremetal compiler, use the standard passes:
- core_cc is used to build the C library;
- as such, it is meant to run on build, not host;
- the final compiler is meant to run on host;

As the current final compiler step can not build a baremetal compiler,
call the core backend from the final step.

NB: Currently, newlib is built during the start_files pass, so we have
to have a core compiler by then... Once we can build the baremetal
compiler from the final cc step, then we can move the newlib build to
the proper step, and then get rid of the core pass-1 static compiler...

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

# This file adds functions to build the C library for bare metal (IE. none)

# Copyright 2008 Yann E. MORIN

# Licensed under the GPL v2. See COPYING in the root of this package

do_libc_get() {

    :

}

do_libc_extract() {

    :

}

do_libc_check_config() {

    :

}

do_libc_start_files() {

    :

}

do_libc() {

    :

}

do_libc_finish() {

    :

}