luaPackages.lux-lua: fix darwin build (#488884)

pkgs/development/lua-modules/lux-lua.nix

@@ -13,6 +13,7 @@
   pkg-config,
   rustPlatform,
   toLuaModule,
+  stdenv,
 }:
 let
   luaMajorMinor = lib.take 2 (lib.splitVersion lua.version);
@@ -62,6 +63,8 @@ toLuaModule (
       LIBGIT2_NO_VENDOR = 1;
       LIBSSH2_SYS_USE_PKG_CONFIG = 1;
       LUX_SKIP_IMPURE_TESTS = 1; # Disable impure unit tests
+      # Allow undefined symbols on Darwin - they must be provided by the Lua runtime
+      RUSTFLAGS = lib.optionalString stdenv.hostPlatform.isDarwin "-C link-arg=-undefined -C link-arg=dynamic_lookup";
     };
 
     buildPhase = ''