Qt: add QT_STATICPLUGIN define as per the qt spec

The QT spec says we should use QT_STATICPLUGIN defined if building a
static plugin.

As we are using out own makefile and not a qt .pro project we have to
define it ourselves.

This is then used to decide if we should import the modules
QWindowsIntegrationPlugin and AccessibleFactory as these are not needed
on a shared build.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/qt4.cpp

@@ -52,8 +52,10 @@
 #ifdef _WIN32 /* For static builds */
  #include <QtPlugin>
  #if HAS_QT5
-  Q_IMPORT_PLUGIN(QWindowsIntegrationPlugin)
-  Q_IMPORT_PLUGIN(AccessibleFactory)
+  #ifdef QT_STATICPLUGIN
+   Q_IMPORT_PLUGIN(QWindowsIntegrationPlugin)
+   Q_IMPORT_PLUGIN(AccessibleFactory)
+  #endif
  #else
   Q_IMPORT_PLUGIN(qjpeg)
   Q_IMPORT_PLUGIN(qtaccessiblewidgets)

modules/gui/qt4/qt4.hpp

@@ -33,6 +33,12 @@
 #include <vlc_interface.h> /* intf_thread_t */
 #include <vlc_playlist.h>  /* playlist_t */
 
+#include <qconfig.h>
+
+#ifdef QT_STATIC
+#define QT_STATICPLUGIN
+#endif
+
 #define QT_NO_CAST_TO_ASCII
 #include <QString>