build-infra: Fix configure output for zip debuginfo check

Andrew Hughes wrote this on the open list:

At the moment, if disable-zip-debug-info is not specified, the configure output is:

checking if we should zip debug-info files...

with no result as $enable_zip_debug_info is unset.

This simple patch makes the option use the more standard AC_ARG_ENABLE form used elsewhere and will
print the default ('yes') when the option is unspecified:

checking if we should zip debug-info files... yes

What actually took longer than the fix was updating the generated files. We seem to have already settled
on autoconf 2.67 for generating the configure script, so my initial attempt threw up a huge number of changes
as the system install is 2.69. I was able to get it down to something closer to what is expected by installing
a local copy of 2.67 but it's still not perfect. I don't know why. I've never been a fan of including generated
files for this reason.

So this script also updates autogen.sh to see if there is an autoconf-2.67 available and use that in preference
to autoconf if it is. I also added a little debug output so we can see which autoconf is being used in autogen.sh.