Ah, thanks! I dug a little more and found that the original test [1] from llvm-toolchain was a little different in the upstream Debian repository. It set the triple to armv7l for armhf hosts.
But I haven't yet found a similar repository on the Raspbian side. I guess I'd expect to find it within their GitHub org, but my searching didn't reveal it.
[1] https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/comm...