buildLuaPackage: fix cross

buildLuaPackage accesses lua.pkgs.luarocks, which became unspliced
at some point.  Let's use callPackage to get it, so we can be sure
it will be spliced.

pkgs/development/interpreters/lua-5/build-lua-package.nix

@@ -2,6 +2,7 @@
 { lib
 , lua
 , wrapLua
+, luarocks
 
 # Whether the derivation provides a lua module or not.
 , luarocksCheckHook
@@ -89,7 +90,7 @@ let
 
   nativeBuildInputs = [
     wrapLua
-    lua.pkgs.luarocks
+    luarocks
   ];
 
   inherit doCheck extraVariables rockspecFilename knownRockspec externalDeps nativeCheckInputs;