Fix using Atom with MSVC
Fix using Atom with MSVC

Summary: Closes https://github.com/facebook/folly/pull/770

Reviewed By: nbronson

Differential Revision: D6991705

Pulled By: yfeldblum

fbshipit-source-id: 9f6ae0e09b436993ee998fe6c5d347121c229489

rklabs/folly,rklabs/folly,facebook/folly,facebook/folly,rklabs/folly,facebook/folly,rklabs/folly,rklabs/folly,facebook/folly,facebook/folly