scripts: update mk-release to cope with the new autoconf framework

Now that ./configure is generated by autoconf, it must be generated
before the release tarball is made. So, we can not simply use hg's
archive, we must post-process it.

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 $?