Explicitly enforce that RequestToken is trivially-destructible
Explicitly enforce that RequestToken is trivially-destructible

Summary:
[Folly] Explicitly enforce that `RequestToken` is trivially-destructible to permit its use as a Meyers Singleton without requiring the use of Leaky Meyers Singleton to avoid destruction-order problems.

(Note: this ignores all push blocking failures!)

Differential Revision: D21533605

fbshipit-source-id: fe334fd5257b1d0a07efd849c4532b28801e54c4

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