Added dummy static class to fix issue with single macro in cpp

The implementation of this dummy class is put in the file with the
single macro defining the UI editor. This will cause the cpp file to
always be compiled.

Fwk/AppFwk/cafPdmCvf/cafPdmUiCoreVec3d.h

@@ -46,6 +46,13 @@
 
 #include "cafPdmCoreVec3d.h"
 
+class Vec3dDummy
+{
+public:
+    Vec3dDummy();
+};
+
+
 namespace caf 
 {
 
@@ -56,6 +63,8 @@ public:
     /// Convert the field value into a QVariant
     static QVariant convert(const cvf::Vec3d& value)
     {
+        static Vec3dDummy dummy;
+
         return PdmValueFieldSpecialization< cvf::Vec3d >::convert(value);
     }