arm_compute v19.02

Change-Id: I853a3ecf38f206da13c1b03640c8adf73c20477c
diff --git a/support/Semaphore.h b/support/Semaphore.h
index 636d5ca..85749e1 100644
--- a/support/Semaphore.h
+++ b/support/Semaphore.h
@@ -46,8 +46,10 @@
     /** Signals a semaphore */
     inline void signal()
     {
-        std::unique_lock<std::mutex> lock(_m);
-        ++_value;
+        {
+            std::lock_guard<std::mutex> lock(_m);
+            ++_value;
+        }
         _cv.notify_one();
     }
     /** Waits on a semaphore */