Looking through clang documentation it looks like my clang is just one version behind (clang 14 is current, and came out just in March).
The problem is actually quite a bit broader. I build root back in April and it worked totally fine, until two days ago, when it started throwing crazy errors when I try to load (see here for more detail). The problems listed in the main post happened when I gave up trying to fix root and just tried to build the most recent version…