Back out "Update folly's source of truth to xplat"
Back out "Update folly's source of truth to xplat"

Summary: Original commit changeset: 6362acb7a668 (D23066827 (https://github.com/facebook/folly/commit/0b3d9d21b7d1496e0b592ee6ce7a687c86c0498f))

Reviewed By: yfeldblum

Differential Revision: D23837145

fbshipit-source-id: 642c1401aea0b01c0c5e53c24b100f5daa600512

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