Make Qt4ProejctManager::MakeStep::run multithreading safe

Change-Id: I416360d35681d2721878cb9fefd861d6e1f209b4
Reviewed-on: http://codereview.qt-project.org/5451
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>

src/plugins/qt4projectmanager/makestep.cpp

@@ -229,9 +229,9 @@ void MakeStep::run(QFutureInterface<bool> & fi)
     }
 
     if (!QFileInfo(m_makeFileToCheck).exists()) {
-        if (!m_clean)
+        if (!ignoreReturnValue())
             emit addOutput(tr("Cannot find Makefile. Check your build settings."), BuildStep::MessageOutput);
-        fi.reportResult(m_clean);
+        fi.reportResult(ignoreReturnValue());
         return;
     }