Set CONSTEXPR_EXCEPT_WIN_CUDA as const while it is not constexpr (#43380)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/42467
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43380
Reviewed By: albanD
Differential Revision: D23278930
Pulled By: pbelevich
fbshipit-source-id: 6ce0bc9fd73cd0ead46c414fdea5f6fb7e9fec3e
