Enable name of threads in release mode.

Naming threads is very useful for release builds.
Enabling only on Linux/Mac for now.
The Windows port is using debugger specific API for setting thread
 names, so it has to remain debug mode only.

Change-Id: I179521f65f215ff038e8230f958f6aa728ea4cbe
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>

src/corelib/thread/qthread_unix.cpp

@@ -287,7 +287,7 @@ void *QThreadPrivate::start(void *arg)
     else
         createEventDispatcher(data);
 
-#if !defined(QT_NO_DEBUG)  && (defined(Q_OS_LINUX) || defined(Q_OS_MAC))
+#if (defined(Q_OS_LINUX) || defined(Q_OS_MAC))
     // sets the name of the current thread.
     QByteArray objectName = thr->objectName().toLocal8Bit();