[racerd] add support for folly's synchronized() {}
[racerd] add support for folly's synchronized() {}

Summary: Folly has a macro SYNCHRONIZED(..) {...} which boils down to the creation/destruction of a LockedPtr object, doing the locking/unlocking.  Add support for that.

Reviewed By: sblackshear

Differential Revision: D7844847

fbshipit-source-id: c7a146d

facebook/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer