Use `ProgramFiles` environment variable on Windows (#39707)
Summary:
'Program Files' does not have to be on disk C (nor necesserily should
be called `Program Files`)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39707
Differential Revision: D21954235
Pulled By: malfet
fbshipit-source-id: 91a9b765cd1bc7e6201dd4b800d45257207010d9
