Fix definition of "__Pyx_CyFunction_USED", which should only be #defined and not have a value.

Cython/Utility/CythonFunction.c

 
 //////////////////// CythonFunctionShared.proto ////////////////////
 
-#define __Pyx_CyFunction_USED 1
+#define __Pyx_CyFunction_USED
 
 #define __Pyx_CYFUNCTION_STATICMETHOD  0x01
 #define __Pyx_CYFUNCTION_CLASSMETHOD   0x02

Cython/Utility/ObjectHandling.c

@@ -2156,7 +2156,7 @@ static CYTHON_INLINE PyObject* __Pyx_PyObject_FastCallDict(PyObject *func, PyObj
     if (f) {
         return f(func, args, nargs, kwargs);
     }
-    #elif __Pyx_CyFunction_USED && CYTHON_BACKPORT_VECTORCALL
+    #elif defined(__Pyx_CyFunction_USED) && CYTHON_BACKPORT_VECTORCALL
     // exclude fused functions for now
     if (__Pyx_CyFunction_CheckExact(func)) {
         __pyx_vectorcallfunc f = __Pyx_CyFunction_func_vectorcall(func);