cc/gcc: Update core_prefix_dir to prefix.

core_prefix_dir is not defined. It should be prefix.

Signed-off-by: Zhenqiang Chen <zhenqiang.chen@linaro.org>

#!/bin/sh

call_to=@@DEFAULT_LD@@

case "${CTNG_LD_IS}" in

    bfd)    call_to=bfd;;

    gold)   call_to=gold;;

esac

exec "${0}.${call_to}" "$@"

exit $?