> CI: build with -Werror on DragonFly BSD, FreeBSD, NetBSD, mingw32, and Ubuntu
This is wrong. Different compilers give different warnings.
And? Critical software like this shall have zero warnings.
Then they shall compile with --no-warnings. Werror only makes the build to fail, without additional benefit for the user.
Failing to build is better than building with undefined behavior.
If you disagree, you can always remove -Werror, at your own risk.