Add support for CMake switches for VS 2019 (#20752)
Summary:
Appending `arch` to the generator name is not supported for VS starting from VS 2019.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20752
Differential Revision: D15436740
Pulled By: ezyang
fbshipit-source-id: 20057aae8f708d82619927bf2cb87dd1bc2df312
