Yeah, that's why every programmer on the project has to be scrupulous about finding and correcting such errors. That's professionalism 101 -- if your team is not keeping the build warning free, things like this slip through.
Things like what, a blatantly obvious bug that would crash virtually every C program running on the system were it not for the fact that it was dead code?
This is practically a documentation bug.
[edit]
I kind of take it back, after mahmud's bzero() joke... out of oniguruma, Python, hexfiend, Apache, nginx, openssl, redis, regexkit, saxon, memcached, subversion, and valgrind, this hypothetical bug would have broken Python, redis, subversion, several apache modules, and memcached. The contents of my codebase/3p directory, FWIW.