Forbid copy-assignment on WakeupFd and Event.

src/unix-adapter/Event.h

@@ -49,6 +49,7 @@ public:
 private:
     // Do not allow copying the Event object.
     Event(const Event &other);
+    Event &operator=(const Event &other);
 
 private:
     HANDLE m_handle;

src/unix-adapter/WakeupFd.h

@@ -32,6 +32,7 @@ public:
 private:
     // Do not allow copying the WakeupFd object.
     WakeupFd(const WakeupFd &other);
+    WakeupFd &operator=(const WakeupFd &other);
 
 private:
     int m_pipeReadFd;