Currently dev-lua/lpeg doesn’t have a pkg-config file, which is surely needed for linking on non-standard paths (Gentoo Prefixes or even just /usr/lib/lua/${lua_version}/). I didn’t manage to find an already existing one (Debian have one, but I can’t find the source, maybe it’s generated) and I failed at writing one.
This is a lua module. Why do you need a pkg-config file for it?
No answer, so closing. Feel free to re-open.