libc/newlib: remove hard-coded "-O"

With hard-coded "-O", users can not customize CFLAGS_FOR_TARGET
by CT_TARGET_CFLAGS. If "-O" is needed, users can input it in
CT_TARGET_CFLAGS. By default, "-Os" is enabled.

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 $?