DELAYLOAD gives linking error in Qt LNK2001: unresolved external symbol
<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>