The parent proposed gating for warnings in the CI, not (by default) on the developer build.

I completely agree with this, as a dev I want to see warnings but I don't always want to have everything perfect from the start. The famous example here is -Wunused-arg. I DON'T want to fight this during development, when I often have prototyping stages where functions remain unimplemented intentionally. I very much want to avoid merging this into master though, so CI gating with -Werror it is.