Bump WINVER 'cuz on default values some required fns are not defined

[tehKaiN]

Part of https://github.com/tangrams/tangram-es/pull/2272

There are some missing API errors when building tangram-es. I could add the updated WINVER as global define add_definitions() but then it collides with GLFW's WINVER override, thus producing compile warnings. The solution is to set it separately for icu and for tangram targets