To use system-wide installed Lua/LuaJIT when linking hslua as a dependency, build/install your package using --constraint="hslua +system-lua" or for LuaJIT: --constraint="hslua +system-lua +luajit". For example, you can install these examples with hslua that uses system-wide LuaJIT like this:

cabal install hslua-examples --constraint="hslua +system-lua +luajit"