bpo-29464: Rename METH_FASTCALL to METH_FASTCALL|METH_KEYWORDS and make (#1955)

the bare METH_FASTCALL be used for functions with positional-only
parameters.
diff --git a/Modules/clinic/_opcode.c.h b/Modules/clinic/_opcode.c.h
index 2f5fd0d..2de8bd7 100644
--- a/Modules/clinic/_opcode.c.h
+++ b/Modules/clinic/_opcode.c.h
@@ -15,17 +15,13 @@
 _opcode_stack_effect_impl(PyObject *module, int opcode, PyObject *oparg);
 
 static PyObject *
-_opcode_stack_effect(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
+_opcode_stack_effect(PyObject *module, PyObject **args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     int opcode;
     PyObject *oparg = Py_None;
     int _return_value;
 
-    if (!_PyArg_NoStackKeywords("stack_effect", kwnames)) {
-        goto exit;
-    }
-
     if (!_PyArg_ParseStack(args, nargs, "i|O:stack_effect",
         &opcode, &oparg)) {
         goto exit;
@@ -39,4 +35,4 @@
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=38f3bf305b3bb601 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=616105b05b55eb45 input=a9049054013a1b77]*/