@bnoordhuis yeah, very good point. currently they don't do anything about visibility (no `-fvisibility=hidden` anywhere).
i could either flip this conditional so `default` is...well, the default, and switch it to `UV_EXTERN_VISIBILITY_HIDDEN`, or define `UV_EXTERN_VISIBILITY_DEFAULT` in the autotools and mingw builds.

win32 has its own separate issues, however, and i was directed by @indutny to not worry about them initially.