libc/glibc: add glibc specifics to the shared code, and use it

Final step at sharing code between glibc and eglibc.
Fall, wall of shame, fall!... :-)

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

#!/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 $?