@lanodan yes, target triple + some sane (i.e. not just a regex) API to match against it would also be good. And yes "GNU" is problematic for that reason, and also I have no idea what to call the various non-GNU userlands seen on Linux in the wild (as seen in: Alpine, Chimera Linux, OpenWrt...) — just calling each one by its own name is not going to be any useful.
Maybe we should file an issue and write a proposal over at Meson's issue tracker.