Fix Windows linkage error.

Libs/PluginFramework/ctkServiceReference.h

@@ -198,7 +198,7 @@ protected:
   template<class S, class T> friend class ctkServiceTrackerPrivate;
   template<class S, class R, class T> friend class ctkPluginAbstractTracked;
 
-  friend uint qHash(const ctkServiceReference&);
+  friend uint CTK_PLUGINFW_EXPORT qHash(const ctkServiceReference&);
 
   ctkServiceReference(ctkServiceRegistrationPrivate* reg);
 

Libs/PluginFramework/ctkServiceRegistration.h

@@ -150,7 +150,7 @@ protected:
   friend class ctkServices;
   friend class ctkServiceReferencePrivate;
 
-  friend uint qHash(const ctkServiceRegistration&);
+  friend uint CTK_PLUGINFW_EXPORT qHash(const ctkServiceRegistration&);
 
   ctkServiceRegistration(ctkServiceRegistrationPrivate* registrationPrivate);