workaround for raw string bug in VS2019 (#28349)
Summary:
reported the problem to microsoft [Developer Community](https://developercommunity.visualstudio.com/content/problem/782476/e-preprocess-to-stdout-cant-handle-raw-string-corr.html)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28349
Differential Revision: D18074620
Pulled By: mingbowan
fbshipit-source-id: 89c2583a0301b1e3055b1f8cd9d493fdb2567b42
