Fix caffe2 build failure on Windows (#20574)
Summary:
Fixes #20568.
Looks like CMake is passing `/MD` when we call `add_library`. We need to fix these with C source files too.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20574
Differential Revision: D15392682
Pulled By: ezyang
fbshipit-source-id: c92034d8725fcec48fd7db6cf5322868e956dc6b
