by Ilya Zakharevich in
http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2001-05/msg01582.html
p4raw-id: //depot/perl@10934
# define XSINTERFACE_CVT(ret,name) ret (*name)()
#endif
#define dXSFUNCTION(ret) XSINTERFACE_CVT(ret,XSFUNCTION)
-#define XSINTERFACE_FUNC(ret,cv,f) ((XSINTERFACE_CVT(ret,cv))(f))
+#define XSINTERFACE_FUNC(ret,cv,f) ((XSINTERFACE_CVT(ret,))(f))
#define XSINTERFACE_FUNC_SET(cv,f) \
CvXSUBANY(cv).any_dptr = (void (*) (pTHXo_ void*))(f)