cc/gcc: add 'cflags' paramater to the core backend

As the core backend is used to generate the bare-metal compiler,
we need to pass it the host CFLAGS.

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

 # Compute Alpha-specific values

 CT_DoArchTupleValues () {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}${CT_ARCH_ALPHA_VARIANT}"

 }