QShortcut: Fix build with -no-feature-whatsthis

Amenends 89f1f14c5e.

Task-number: QTBUG-79638
Change-Id: I95c73d5004f234e27967a68d2b770c177fc1ff8d
Reviewed-by: Nodir Temirkhodjaev <nodir.temir@gmail.com>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/kernel/qshortcut.cpp

@@ -410,10 +410,14 @@ public:
 
 bool QShortcutPrivate::handleWhatsThis()
 {
+#if QT_CONFIG(whatsthis)
     const bool result = QWhatsThis::inWhatsThisMode();
     if (result)
         QWhatsThis::showText(QCursor::pos(), sc_whatsthis);
     return result;
+#else
+    return false;
+#endif
 }
 
 /*!