cc/gcc: build bare-metal gcc statically

- add a new parameter to do_cc_core: build_statically=[yes|no]
- pass build_statically=yes in core_pass_2 when doing bare_metal
- fix handling the static / static libstdc++ / static complibs stuff
- add a commment to keep both blocks (in core and final) in sync

Signed-off-by: "Bryan Hundven" <bryanhundven@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

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