Cocoa integration - fix Qt::WindowFullscreenButtonHint

Window collection behavior changed from OS X <= 10.9 to 10.10 to 10.11:
- the default behavior (0) included fullscreen button before 10.10, did not include
in 10.10, and now it's again included.
- it's not enough to exclude fullscreen - since the defualt is 0,
 0 & ~fullscreen does not help - we also have to set fullscreen
 auxiliary.

Task-number: QTBUG-48759
Change-Id: If427bd5cfa5c3cefc71f09dae7baa0d232601ee4
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@theqtcompany.com>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -885,10 +885,13 @@ void QCocoaWindow::setWindowFlags(Qt::WindowFlags flags)
         Qt::WindowType type = window()->type();
         if ((type & Qt::Popup) != Qt::Popup && (type & Qt::Dialog) != Qt::Dialog) {
             NSWindowCollectionBehavior behavior = [m_nsWindow collectionBehavior];
-            if (flags & Qt::WindowFullscreenButtonHint)
+            if (flags & Qt::WindowFullscreenButtonHint) {
                 behavior |= NSWindowCollectionBehaviorFullScreenPrimary;
-            else
+                behavior &= ~NSWindowCollectionBehaviorFullScreenAuxiliary;
+            } else {
+                behavior |= NSWindowCollectionBehaviorFullScreenAuxiliary;
                 behavior &= ~NSWindowCollectionBehaviorFullScreenPrimary;
+            }
             [m_nsWindow setCollectionBehavior:behavior];
         }
         setWindowZoomButton(flags);