scoped_timer: wait for timer thread before main thread continues (#4803)

src/util/scoped_timer.cpp

@@ -34,7 +34,7 @@ struct scoped_timer_state {
     std::timed_mutex m_mutex;
     event_handler * eh;
     unsigned ms;
-    int work;
+    std::atomic<int> work;
     std::condition_variable_any cv;
 };
 
@@ -102,6 +102,8 @@ public:
 
     ~imp() {
         s->m_mutex.unlock();
+        while (s->work == 1)
+            std::this_thread::yield();
     }
 };