CMake: Turn MSVC optimizations up to 11

This improves performance on GPU bound applications by about 30% to 50% depending on the configuration:

 | master | cmake-opts
--- | --- | ---
Release | 7.4212 s | 5.6802 s
RelWithDebInfo | 8.9296 s | 5.731 s
Then shouldn't it only be required IF Qt is found?