Change LuaJIT to use GUIX_LUA_PATH and GUIX_LUA_CPATH to construct the default
LUA_PATH and LUA_CPATH, instead of using hard-coded paths that Guix doesn't
populate.

These paths don't use Lua's usual '?' path wildcard, and thus are compatible
with Guix's search-paths mechanism.

This patch uses functions defined in lua-5.x-search-path-helpers.patch.

--- a/src/lib_package.c
+++ b/src/lib_package.c
@@ -590,6 +590,8 @@
   NULL
 };
 
+#include "./guixpaths.c"
+
 LUALIB_API int luaopen_package(lua_State *L)
 {
   int i;
@@ -612,8 +667,16 @@
   lua_getfield(L, LUA_REGISTRYINDEX, "LUA_NOENV");
   noenv = lua_toboolean(L, -1);
   lua_pop(L, 1);
-  setpath(L, "path", LUA_PATH, LUA_PATH_DEFAULT, noenv);
-  setpath(L, "cpath", LUA_CPATH, LUA_CPATH_DEFAULT, noenv);
+
+  /* Calculate default LUA_PATH and LUA_CPATH values from their
+     corresponding GUIX_ environment variables */
+  const char* default_path = guix_path(L); // push default_path
+  const char* default_cpath = guix_cpath(L); // push default_cpath
+  lua_pushvalue(L, -3); // copy the old head of the stack back to the top
+  setpath(L, "path", LUA_PATH, default_path, noenv);
+  setpath(L, "cpath", LUA_CPATH, default_cpath, noenv);
+  lua_pop(L, 3); // pop our three working values back off the stack
+
   lua_pushliteral(L, LUA_PATH_CONFIG);
   lua_setfield(L, -2, "config");
   luaL_findtable(L, LUA_REGISTRYINDEX, "_LOADED", 16);