Dependencies for lua-2.1.0

Use the system-wide Lua instead of the bundled copy.

Compile Lua with -DLUA_USE_APICHECK.

Compile Lua with -DLUA_32BITS

Allow optimizations which make Lua's garbage collection potentially unsafe; enabling this should be safe if there are no callbacks into Haskell during Lua garbage collection cycles. The flag should be *disabled* if Lua objects can have Haskell finalizers, i.e., __gc metamethods that call Haskell function.

Add all symbols to dynamic symbol table; disabling this will make it possible to create fully static binaries, but renders loading of dynamic C libraries impossible.

Use pkg-config to discover library and include paths. Setting this flag implies `system-lua`.

Don't use CAPI to determine the names of certain registry key names but use hard coded values instead. This flag is required when compiling against Lua 5.3.3 or earlier, as those versions do not expose the necessary information in the lauxlib.h header file. Setting this flag should usually be unproblematic, except if the used Lua version has been patched heavily.