CMakePM: Add "[cmake] " prefix to all output messages

With this one could easily filter the "[cmake] " messages from all the
messages in the "Generate Messages" pane.

Change-Id: I690650f0ccb0372c9361b95cfec41809737720d7
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/cmakeprojectmanager/cmakeprocess.h

@@ -43,4 +43,7 @@ private:
     QElapsedTimer m_elapsed;
 };
 
+QString addCMakePrefix(const QString &str);
+QStringList addCMakePrefix(const QStringList &list);
+
 } // CMakeProjectManager::Internal