Add copy logic for LibTorch to avoid issues on Windows (#25556)
Summary:
This should work both on VS and Ninja.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25556
Differential Revision: D17162045
Pulled By: ezyang
fbshipit-source-id: 18c3d62e9ba93bf603f3a5310087fac77be4a974
