title: DELAYLOAD gives linking error in Qt LNK2001: unresolved external symbol
body: <p>I am trying to use <code>DELAYLOAD</code> flag in Qt creator. Here is minimal code which explains my problem:
  In <code>pro</code> file:</p>
  <pre><code>QT       += core gui
  greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
  
  TARGET = DelayLoad
  TEMPLATE = app
  CONFIG+=qwt
  
  SOURCES += main.cpp\
      mainwindow.cpp
  
  HEADERS  += mainwindow.h
  
  win32: LIBS += -L$$PWD/../../../../../qwt-6.1.2/lib/ -lqwt
  INCLUDEPATH += $$PWD/../../../../../qwt-6.1.2/include
  DEPENDPATH += $$PWD/../../../../../qwt-6.1.2/include
  
  win32: QMAKE_LFLAGS_RELEASE += /DELAYLOAD:qwt.dll
  </code></pre>
  <p>In <code>mainwindow.cpp</code>:</p>
  <pre><code>#include &quot;mainwindow.h&quot;
  #include &lt;QPushButton&gt;
  #include &quot;qwt_plot.h&quot;
  
  MainWindow::MainWindow(QWidget *parent)
      : QMainWindow(parent)
  {
      QPushButton *button = new QPushButton(&quot;replace by plot&quot;);
      connect(button, SIGNAL(clicked(bool)),this,SLOT(buttonClicked()));
      this-&gt;setCentralWidget(button);
  }
  
  MainWindow::~MainWindow()
  {
  }
  
  void MainWindow::buttonClicked()
  {
      QwtPlot *plot = new QwtPlot();
      this-&gt;setCentralWidget(plot);
  }
  </code></pre>
  <p>This gives the following error:</p>
  <blockquote>
  <p>qwt.lib(qwt.dll):-1: error: LNK2001: unresolved external symbol __delayLoadHelper2</p>
  </blockquote>
  <p>I clicked several on <code>Run qmake</code>, <code>Clear</code>, <code>Rebuild</code>. That does not solve initial problem. I am using 'Qt 5.4.2' with <code>MSVC 2013 64 bit</code> compiler</p>