contrib: qt: Don't require OpenGL on the host, patch missing includes

By building with PCH disabled (contrary to what Qt otherwise uses), this build config managed to expose a missing include in Qt (when I tested with a libc++ setup with _LIBCPP_REMOVE_TRANSITIVE_INCLUDES enabled, which makes it much more strict with requiring to include all the right headers).

I'll update the second commit with a better reference to the final commit once it lands upstream (it is currently accepted in review).