add SAL_WARN_UNUSED to css::uno::WeakReference and SvCompatWeakRef

Change-Id: Idb784d398ed22f2291f1beaffb82f68642d68bcd

include/cppuhelper/weakref.hxx

@@ -119,7 +119,7 @@ protected:
     @tparam interface_type type of interface
 */
 template< class interface_type >
-class WeakReference : public WeakReferenceHelper
+class SAL_WARN_UNUSED WeakReference : public WeakReferenceHelper
 {
 public:
     /** Default ctor.  Creates an empty weak reference.

include/tools/ref.hxx

@@ -183,7 +183,7 @@ public:
 /** We only have one weak reference in LO, in include/sfx2/frame.hxx, class SfxFrameWeak.
 */
 template<typename T>
-class SvCompatWeakRef
+class SAL_WARN_UNUSED SvCompatWeakRef
 {
     tools::SvRef< SvCompatWeakHdl<T> > _xHdl;
 public: