iOS: Don't reference QMacStyle from QStyleOption as we don't build it

QMacStyle is not buildt as a part of iOS. So make sure we dont
reference it from QStyleOption

Change-Id: I98e779c576d0607402e45a19b457144a6bdfc73b
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>

src/widgets/styles/qstyleoption.cpp

@@ -206,7 +206,7 @@ void QStyleOption::init(const QWidget *widget)
     if (!(state & QStyle::State_Active) && !qt_mac_can_clickThrough(widget))
         state &= ~QStyle::State_Enabled;
 #endif
-#ifdef Q_OS_MAC
+#if defined(Q_OS_MAC) && !defined(Q_OS_IOS)
     switch (QMacStyle::widgetSizePolicy(widget)) {
     case QMacStyle::SizeSmall:
         state |= QStyle::State_Small;