fix -Wsuggest-override and -Wsuggest-destructor-override

Summary:
```
folly/executors/InlineExecutor.h:29:11: error: '~InlineLikeExecutor' overrides a destructor but is not marked 'override' [-Werror,-Wsuggest-destructor-override]
  virtual ~InlineLikeExecutor() {}
          ^
folly/Executor.h:57:11: note: overridden virtual function is here
  virtual ~Executor() {}
          ^
In file included from tupperware/agent/system/Mounts.cpp:18:
In file included from folly/futures/Future.h:36:
In file included from folly/fibers/Baton.h:297:
In file included from folly/fibers/Baton-inl.h:19:
folly/fibers/FiberManagerInternal.h:588:10: error: 'timeoutExpired' overrides a member function but is not marked 'override' [-Werror,-Wsuggest-override]
    void timeoutExpired() noexcept { run(); }
         ^
folly/io/async/HHWheelTimer.h:95:18: note: overridden virtual function is here
    virtual void timeoutExpired() noexcept = 0;
                 ^
In file included from tupperware/agent/system/Mounts.cpp:18:
In file included from folly/futures/Future.h:36:
In file included from folly/fibers/Baton.h:297:
In file included from folly/fibers/Baton-inl.h:19:
folly/fibers/FiberManagerInternal.h:589:10: error: 'callbackCanceled' overrides a member function but is not marked 'override' [-Werror,-Wsuggest-override]
    void callbackCanceled() noexcept {}
         ^
folly/io/async/HHWheelTimer.h:100:18: note: overridden virtual function is here
    virtual void callbackCanceled() noexcept { timeoutExpired(); }
                 ^
3 errors generated.
```

Reviewed By: simpkins

Differential Revision: D27988235

fbshipit-source-id: 799484c52f89fa20f647ff0801b8d136b657b395

folly/executors/InlineExecutor.h

@@ -26,7 +26,7 @@ namespace folly {
 
 class InlineLikeExecutor : public virtual Executor {
  public:
-  virtual ~InlineLikeExecutor() {}
+  virtual ~InlineLikeExecutor() override {}
 };
 
 /// When work is "queued", execute it immediately inline.

folly/fibers/FiberManagerInternal.h

@@ -585,8 +585,8 @@ class FiberManager : public ::folly::Executor {
 
    private:
     FiberManager& fiberManager_;
-    void timeoutExpired() noexcept { run(); }
-    void callbackCanceled() noexcept {}
+    void timeoutExpired() noexcept override { run(); }
+    void callbackCanceled() noexcept override {}
   };
 
   FibersPoolResizer fibersPoolResizer_;

folly/logging/LogStream.h

@@ -64,7 +64,7 @@ class LogStream : public std::ostream {
   // bloat, with minimal benefit--for debug log statements these never even get
   // called in the common case where the log statement is disabled.
   explicit LogStream(LogStreamProcessor* processor);
-  ~LogStream();
+  ~LogStream() override;
 
   bool empty() const { return buffer_.empty(); }