Replace Autotools-based build system by CMake.

Hi there,

The subject says what I’m trying to do but I’m not even sure that it’s
sane to try to do it.

About a year ago, for my sins, I became the maintainer of BackupPC:

The project is in reasonable shape but frankly the build systems that
I inherited were badly in need of an overhaul.

For the past few days to get a toe in the water I’ve been playing with
CMake to try to replace the Autotools parts of the BackupPC-XS package
with a CMakeLists.txt. I managed to produce something that will build
a rough approximation to a Perl XS library module, but it’s a long way
from running at the moment - I need to get the linking figured out.

Anyway, to begin with: is what I’m trying to do here sane?