Draft: contrib/rpm: enable -Werror on --with debug instead of --with test

The test bcond is used to make test suite failure terminate the %check phase. That should generally be done for distro builds.

What the distro builds shouldn't do is terminate the build on compiler warnings, because they're fairly likely to appear on toolchain updates without indicating actual bugs.

However, currently that's precisely what do we do now.

Let's use -Werror on debug builds instead. They are intentionally made more prone to fail (e.g. trip more runtime assertions) because failures can be more rapidly addressed and don't affect distro builds.