Preliminary changes for PowerPC 64-bits support

These changes allow to build SlapOS on Debian Buster ppc64el.

The PowerPC 64-bits little endian platform appeared more recently into autoconf and therefore needed updated config.sub and config.guess files.

Somehow these only needed to be patched on autoconf itself which is quite dated (2012), and libyaml that does not ship it's own config.sub and config.guess files. Other components built fine out of the box.

config.sub and config.guess files were taken from Debian Buster itself. More information at: https://wiki.debian.org/AutoTools/autoconf

This merge request would have to be backported to previous releases in the case components reference older releases of SlapOS, which, if I understand correctly, is the case some times.