cc/gcc: rename the core backend function

Rename the core backend function to do_cc_core_backend, to
make it explicit it is a backend.

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

 # Compute M68k-specific values

 CT_DoArchTupleValues() {

     :

 }