Ensured explicit check for undefined references on shared objects

- On certain platforms, shared objects will be built without linker
  errors even if they have undefined references (but they'll fail to
  load if those references can't be found at runtime).
- This resolves issues with plugins that on linux seem to compile, but
  won't load (or will lead completely unpredictable results) because
  they use symbols that may not exist. Special thanks to oss10110 for
  bringing it up.

Signed-off-by: Haru <haru@dotalux.com>