Use compact_once_flag for DelayedInit
Use compact_once_flag for DelayedInit

Summary: Use the 1 byte version of `once_flag` such that there is no more memory overhead than `Optional`.

Reviewed By: andriigrynenko

Differential Revision: D25909346

fbshipit-source-id: 1bb2f41200917ba58b20815bfafe3314137e9680

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