Cleanup debug info switches with MSVC (#39703)
Summary:
Switch off `/Z7` so that we don't generate debug info in Release and MinSizeRel builds, so that we will probably get smaller static libraries and object files and faster build time
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39703
Differential Revision: D21960684
Pulled By: ezyang
fbshipit-source-id: 909a237a138183591d667885b13fc311470eed65
