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 Alpha-specific values

 CT_DoArchTupleValues () {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}${CT_ARCH_ALPHA_VARIANT}"

 }