Remove constexpr for NVCC on Windows (#40675)
Summary:
They are not well supported. Fixes https://github.com/pytorch/pytorch/issues/40393 and https://github.com/pytorch/pytorch/issues/39394.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40675
Differential Revision: D22286031
Pulled By: ezyang
fbshipit-source-id: 7e309916ae21cd3909ee6466952ba89847c74d71
