make the fast-call signature test compatible with Stackless Python

Add METH_STACKLESS to the bit mask used to test the call signature.

Cython/Utility/ModuleSetupCode.c

@@ -388,6 +388,11 @@ class __Pyx_FakeReference {
   #define Py_TPFLAGS_HAVE_FINALIZE 0
 #endif
 
+#ifndef METH_STACKLESS
+  // already defined for Stackless Python (all versions) and C-Python >= 3.7
+  // value if defined: Stackless Python < 3.6: 0x80 else 0x100
+  #define METH_STACKLESS 0
+#endif
 #if PY_VERSION_HEX <= 0x030700A3 || !defined(METH_FASTCALL)
   // new in CPython 3.6, but changed in 3.7 - see
   // positional-only parameters:
@@ -407,7 +412,7 @@ class __Pyx_FakeReference {
 #endif
 #if CYTHON_FAST_PYCCALL
 #define __Pyx_PyFastCFunction_Check(func) \
-    ((PyCFunction_Check(func) && (METH_FASTCALL == (PyCFunction_GET_FLAGS(func) & ~(METH_CLASS | METH_STATIC | METH_COEXIST | METH_KEYWORDS)))))
+    ((PyCFunction_Check(func) && (METH_FASTCALL == (PyCFunction_GET_FLAGS(func) & ~(METH_CLASS | METH_STATIC | METH_COEXIST | METH_KEYWORDS | METH_STACKLESS)))))
 #else
 #define __Pyx_PyFastCFunction_Check(func) 0
 #endif

Cython/Utility/ObjectHandling.c

@@ -1557,7 +1557,7 @@ static int __Pyx_TryUnpackUnboundCMethod(__Pyx_CachedCFunction* target) {
     {
         PyMethodDescrObject *descr = (PyMethodDescrObject*) method;
         target->func = descr->d_method->ml_meth;
-        target->flag = descr->d_method->ml_flags & ~(METH_CLASS | METH_STATIC | METH_COEXIST);
+        target->flag = descr->d_method->ml_flags & ~(METH_CLASS | METH_STATIC | METH_COEXIST | METH_STACKLESS);
     }
 #endif
     return 0;
@@ -2111,7 +2111,7 @@ static CYTHON_INLINE PyObject * __Pyx_PyCFunction_FastCall(PyObject *func_obj, P
     int flags = PyCFunction_GET_FLAGS(func);
 
     assert(PyCFunction_Check(func));
-    assert(METH_FASTCALL == (flags & ~(METH_CLASS | METH_STATIC | METH_COEXIST | METH_KEYWORDS)));
+    assert(METH_FASTCALL == (flags & ~(METH_CLASS | METH_STATIC | METH_COEXIST | METH_KEYWORDS | METH_STACKLESS)));
     assert(nargs >= 0);
     assert(nargs == 0 || args != NULL);