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>

 # Compute sparc-specific values

 CT_DoArchTupleValues() {

     # That's the only thing to override

     if [ "${CT_ARCH_64}" = "y" ]; then

         CT_TARGET_ARCH="${CT_ARCH}64"

     fi

 }