Add support for building with mingw-w64 GCC. Fix warnings

Pdf4QtViewerPlugins/AudioBookPlugin/AudioBookPlugin.pro

@@ -20,18 +20,20 @@ DEFINES += AUDIOBOOKPLUGIN_LIBRARY
 
 QT += gui widgets
 
+include(../../Pdf4Qt.pri)
+
 LIBS += -L$$OUT_PWD/../..
 
 LIBS += -lPdf4QtLib
 
-QMAKE_CXXFLAGS += /std:c++latest /utf-8
+win32-*g++: {
+    LIBS += -lole32 -lsapi
+}
 
 INCLUDEPATH += $$PWD/../../Pdf4QtLib/Sources
 
 DESTDIR = $$OUT_PWD/../../pdfplugins
 
-CONFIG += c++11
-
 SOURCES += \
     audiobookcreator.cpp \
     audiobookplugin.cpp \

Pdf4QtViewerPlugins/AudioBookPlugin/audiobookcreator.cpp

@@ -18,6 +18,7 @@
 #include "audiobookcreator.h"
 
 #ifdef Q_OS_WIN
+#include <windows.h>
 #include <sapi.h>
 #if defined(PDF4QT_USE_PRAGMA_LIB)
 #pragma comment(lib, "ole32")