[luatex] Linking to C libraries / TL2017 / FFI

[Michal Hoftich]

Hi Patrick

> > it probably is mostly a platform issue because on windows one cal already load libraries for years (it was recently broken for a while which made users who use that complain)
> 
> still curious if anybody can confirm if this works on Mac & Linux.

It works for me Fedora. With correct package.cpath I can even use
modules installed using Luarocks. The only problem is that Fedora uses
Lua 5.3 and LuaTeX uses Lua 5.2, so some libraries fail because of
version mismatch. 

Best regards,
Michal