configure: use autoconf to generate configure

Create configure.ac, an autoconf script to generate ./configure
This will be needed by a subsequent patch to properly handle
--build and --host, and more tests, when the kconfig stuff will
be installed pre-built.

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

 #!/bin/sh

 set -e

 printf "Running autoconf...\n"

 autoconf -Wall --force

 printf "Done. You may now run:\n    ./configure\n"