cc/gcc: fix recent gcc build

This fix missed conversion of CT_GCC_USE_* to CT_CC_GCC_USE_*.

Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>

 reporter_name="Remy Bohmer"

 reporter_url="linux@bohmer.net"

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