This is conceptually interesting to me. In practice, I don't see us using
this in Ubuntu. We have per-architecture differences from Debian (ppc64el
building with -O3 by default; riscv64 being a release architecture where it
isn't in Debian) that make it interesting to pick up on per-architecture
build failures caught by -Werror and not without. But it's not practical to
do CI -Werror builds; when we do out-of-archive rebuilds for all
architectures, it's a significant committment of resources and each rebuild
takes about a month to complete (on the slowest archs). And to be able to
effectively analyze build results to identify Werror-related failures with
high signal would require two parallel builds, one with and without the
flag, built against the same baseline.