Fix folly::Singleton to work in dynamically linked binaries

Fix folly::Singleton to work in dynamically linked binaries

Summary:This implements StaticSingletonManager which is then used to create all leaked Meyers singletons.

StaticSingletonManager is a singleton itself, which is created in a separate compilation unit (Singleton.cpp) and so we can be sure that other compilation units will always see a single instance of StaticSingletonManager, even if linked dynamically.

StaticSingletonManager then keeps a dictionary of typeid -> object pointer, which is used to de-duplicate same singleton being re-created from different compilation units (linked dynamically), usually because of code inlining.

override-unit-failures

Reviewed By: yfeldblum

Differential Revision: D2913027

fb-gh-sync-id: 1f5015a79a7a8297ebf5f0fe3fd0cc7eb44f706b
shipit-source-id: 1f5015a79a7a8297ebf5f0fe3fd0cc7eb44f706b