[OpenMP][OMPT] Fix accidental concatenation of notifications

Fix the rather common occurrence of concatenated notifications.
Especially the asynchronously generated trace records could potentially
'interleave' just between putting the notification and the newline char.

Change-Id: I34ddc10660788018d31b4dc9b4f02f677c44cbf3

Author: mhalk

openmp/libomptarget/test/ompTest/src/OmptAsserter.cpp

@@ -268,5 +268,8 @@ void OmptEventReporter::notify(OmptAssertEvent &&AE) {
   if (!isActive() || isSuppressedEventType(AE.getEventType()))
     return;
 
-  OutStream << AE.toString() << std::endl;
+  // Prepare notification, containing the newline to avoid stream interleaving.
+  auto Notification{AE.toString()};
+  Notification.push_back('\n');
+  OutStream << Notification;
 }