Having debugged my share of autoconf setups..I assumed it
had to be a new M4 and not the ancient quirky GNU M4 thing because no one in their right mind would wish M4 (and related GNU autoconfig / autconf) on any other sentient beings.
It’d be like saying - “hey, I’m starting a new project and trying to pick between ed, sed, or awk. Whatcha think”? Def not.