Debugging: Enable Windows debugging for clang tools

On Windows the debugging of clang tools is not working due to the
nature of how processes are started.

This makes it possible to use DebugViewer or DebugViewPP

Change-Id: I2c1e4bb7a8fafd6f07570e5d2ba4df5b44e9d44d
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/tools/clangrefactoringbackend/clangrefactoringbackendmain.cpp

@@ -131,8 +131,10 @@ struct Data // because we have a cycle dependency
 };
 
 #ifdef Q_OS_WIN
+extern "C" void OutputDebugStringW(const wchar_t* msg);
 static void messageOutput(QtMsgType type, const QMessageLogContext &, const QString &msg)
 {
+    OutputDebugStringW(msg.toStdWString().c_str());
     std::wcout << msg.toStdWString() << std::endl;
     if (type == QtFatalMsg)
         abort();