a small CMakeLists.txt fix

[tuotuoxp]

try to fix a link error under Windows by wrapping lua-related configurations with PROVIDE_LUA_ENGINE

[hughperkins]

Even if easycl doesnt provide lua itself, the templater still needs to work. For example, when linking with Torch, Torch provides the lua engine, hence easycl does not include it. However, for Torch, the templater is very much required.

If you want to disable the templater, I think that should be a new option.