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>

 # Configuration file for sstrip tool facility

 if OBSOLETE && ! BACKEND && ARCH_BINFMT_ELF

 comment "sstrip"

 config SSTRIP

     bool

     prompt "sstrip (OBSOLETE)"

     help

       The sstrip utility, to maximise the striping of ELF binaries

       (executables and libraries).

       Buildroot version, forked off the original from ELFkickers.

       This one is somewhat maintained by the buildroot guys.

       Supports big-endian systems.

       NOTE! Please read.

         sstrip is now deprecated in crosstool-NG, as it has a few

         shortcomings. For example: it breaks for PPC targets, it

         does not build on non-ELF hosts (eg. mingw32, MacOS-X...).

 endif