Wish: Make possible cross-compiling of Qt application using MinGW

[Dmitry Tantsur]

Now when you try to build mingw-win32 application under Ubuntu which uses qt you'll see something like:

mingw -c -pipe -g -Wall -W -D_REENTRANT -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -Ibuild -Ibuild -o build/mainwindowimpl.o src/mainwindowimpl.cpp
In file included from /usr/include/qt4/QtGui/qwidget.h:45,
                 from /usr/include/qt4/QtGui/qmainwindow.h:45,
                 from /usr/include/qt4/QtGui/QMainWindow:1,
                 from src/mainwindowimpl.h:4,
                 from src/mainwindowimpl.cpp:1:
/usr/include/qt4/QtGui/qwindowdefs.h:110:35: error: QtGui/qwindowdefs_win.h: No such file or directory
In file included from /usr/include/qt4/QtGui/qwidget.h:45,
                 from /usr/include/qt4/QtGui/qmainwindow.h:45,
                 from /usr/include/qt4/QtGui/QMainWindow:1,
                 from src/mainwindowimpl.h:4,
                 from src/mainwindowimpl.cpp:1:
/usr/include/qt4/QtGui/qwindowdefs.h:138: error: ‘WId’ was not declared in this scope
/usr/include/qt4/QtGui/qwindowdefs.h:138: error: template argument 1 is invalid
/usr/include/qt4/QtGui/qwindowdefs.h:138: error: invalid type in declaration before ‘;’ token
In file included from /usr/include/qt4/QtGui/qwidget.h:47,
                 from /usr/include/qt4/QtGui/qmainwindow.h:45,
                 from /usr/include/qt4/QtGui/QMainWindow:1,
                 from src/mainwindowimpl.h:4,
                 from src/mainwindowimpl.cpp:1:
/usr/include/qt4/QtGui/qpaintdevice.h:87: error: ‘HDC’ does not name a type
/usr/include/qt4/QtGui/qpaintdevice.h:88: error: ‘HDC’ has not been declared

and so on.