You don't need a complex obscure build system for most C code. There's a lot of historical baggage here, but many projects (including xz, I suspect) can get away with a fairly straight-forward Makefile. Double so when using some GNU make extensions.
Thanks for that post, I wish people stopped pushing ever so more complicated build systems, opaque, non-backward compatible between their own versions when a 2 pages Makefile would work just fine, and still work in 20 years time.