scripts: fix download from sourceforge

It seems sourceforge changed yet again the way to download files.
This time, no longer use their 'mesh' thingy, and hard-code the
server to use in the URL... Sigh... :-(

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 $?