`makepkg` extra args

makepkg has this neat feature allowing it to consume extra args defined in key=value scheme i.e: makepkg CPU=haswell and most aur-helpers allow to pass those with a cli switch e.g: aurutils --margs=CPU=hasswell, yay/paru --mflas=CPU=haswell

Could we leverage this functionality? I could concoct a PR if you're interested.