I worked at Apple for a long time. The OS gets fully recompiled regularly.
A simultaneous total world build is relatively rare (is that needed here?), but it does happen. Sometimes new compiler versions or features need this.
I dunno if that's sensitive information, but how long did a build usually take?
Hm that leaves more questions for me. Why does this path not have bounds checking, is think perhaps a limit of the clang flag or is it more simply a mistake of omission on apples part. Either way it seems like a bad look. I wish we’d get a post mortem