Fix Z7_MSVC_OVERRIDE for C source files (#24389)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/24145#issuecomment-521507234
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24389
Differential Revision: D16828222
Pulled By: ezyang
fbshipit-source-id: dcf652fbd8b8945c71993e9b99394e18ac542e6b
