heavily rework lua discovery and linking, needs testing but it's more similar to what we do for other libraries now

oops, haskell uses gcc to link, correctly pass flags

since shared libs are now our friends, let's optimise them

aaaaand let's not forget about lua, which has also a slightly revised build process

drop the '_'

and now also avwrapper can be shared/static, add visibility to its exported functions, drop (needed only when static)