After looking at the most recent responses and thinking "Hmm, I thought we already implicated -w as the culprit. Why are these comments repeating stuff...", I realized that I had discussed this in CB, and did not update this conversation with the resolution.

Yes, -w was causing problems. It was a cargo cultism, brought forward in a local code template (written by me, no less), the content of the static parts which has been mostly ignored since originally authored. Once the -w was removed from the shebang line, all is well with the world, warning scope is proper, birds are singing...

In all, thanks everyone for your help.