Make it possible for users for select /Zi or /ZI over /Z7 when using MSVC (#18790)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/18701.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18790
Differential Revision: D14748195
Pulled By: ezyang
fbshipit-source-id: e50df1b5ca199a88d7b5ea3ea45d25d23cd31a27
