cc/gcc: simplify calls to core backend

The core backend is going to have more parameters in the upcoming
patches, so it will be a bit complex to handle.

Introduce an array-variable that is filled by the different code-paths
with the required values.

This makes the code easier to read and maintain.

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

reporter_name="Remy Bohmer"

reporter_url="linux@bohmer.net"

reporter_comment="Example for building a toolchain for m68000 bare metal targets"