Always define FOLLY_HAS_COROUTINES
Always define FOLLY_HAS_COROUTINES

Summary: To enable building with -Werror,-Wundef.

Reviewed By: guangyfb

Differential Revision: D18850905

fbshipit-source-id: 95555781fec991eac119c95a6a6cd7751b5ba742

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