QmlDesigner: fixes warning

We get a warning if the operator is used from another module.

Change-Id: Ib798037cb6e16fbb2c3fb4fb61d9445a0d5cd93d
Reviewed-by: Marco Bubke <marco.bubke@digia.com>

src/plugins/qmldesigner/designercore/include/metainfo.h

@@ -61,7 +61,7 @@ class QMLDESIGNERCORE_EXPORT MetaInfo
     friend class QmlDesigner::Internal::ModelPrivate;
     friend class QmlDesigner::Internal::MetaInfoReader;
     friend class QmlDesigner::Internal::SubComponentManagerPrivate;
-    friend bool operator==(const MetaInfo &, const MetaInfo &);
+    friend QMLDESIGNERCORE_EXPORT bool operator==(const MetaInfo &, const MetaInfo &);
 
 public:
     MetaInfo(const MetaInfo &metaInfo);