Fix GCC 4.7 errors

GCC 4.7.2 fail overriding constructors defined with virtual and default.
Debian build also fails linking  without -lrt.
INT64_C is not defined on Debian with 4.7.2. "ll" should be enough.

Change-Id: Ia779f094ed64fc3b1941429485e81520d017c2f5
Reviewed-on: https://weave-review.googlesource.com/1671
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
diff --git a/src/notification/notification_delegate.h b/src/notification/notification_delegate.h
index 719d76d..263c2f3 100644
--- a/src/notification/notification_delegate.h
+++ b/src/notification/notification_delegate.h
@@ -24,7 +24,7 @@
   virtual void OnDeviceDeleted(const std::string& cloud_id) = 0;
 
  protected:
-  virtual ~NotificationDelegate() = default;
+  virtual ~NotificationDelegate() {}
 };
 
 }  // namespace weave