Don't throw in the Watchdog destructor

Summary: As-of C++11, destructors are assumed to be `noexcept` unless explicitly marked otherwise. `Watchdog`'s destructor throws, so switch it to a `LOG(FATAL)` instead.

Reviewed By: andriigrynenko

Differential Revision: D3672621

fbshipit-source-id: 5224ecf85d101462e02e12da257e033bab4db1a1

folly/test/SingletonTestStructs.h

@@ -39,7 +39,7 @@ struct Watchdog {
 
   ~Watchdog() {
     if (creation_order().back() != this) {
-      throw std::out_of_range("Watchdog destruction order mismatch");
+      LOG(FATAL) << "Watchdog destruction order mismatch";
     }
     creation_order().pop_back();
   }