QSharedPointer: Fix build error for cross-built tools

Guard friend declaration within QT_NO_QOBJECT.
Amends 28ce318fcb.

Fixes: QTBUG-76056
Change-Id: I14fbe5457c16e8a366fecdc0a356b68b8609848b
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

src/corelib/tools/qsharedpointer_impl.h

@@ -678,9 +678,11 @@ public:
 #else
     template <class X> friend class QSharedPointer;
     template <class X> friend class QPointer;
+#  ifndef QT_NO_QOBJECT
     template<typename X>
     friend QWeakPointer<typename std::enable_if<QtPrivate::IsPointerToTypeDerivedFromQObject<X*>::Value, X>::type>
     qWeakPointerFromVariant(const QVariant &variant);
+#  endif
     template<typename X>
     friend QPointer<X>
     qPointerFromVariant(const QVariant &variant);