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>

 reporter_name="Alexander BIGGA"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-07/msg00000.html"

 reporter_comment=""