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/_datetimemodule.c.h b/Modules/clinic/_datetimemodule.c.h
index 1ffe133..3887bba 100644
--- a/Modules/clinic/_datetimemodule.c.h
+++ b/Modules/clinic/_datetimemodule.c.h
@@ -14,7 +14,7 @@
 "If no tz is specified, uses local timezone.");
 
 #define DATETIME_DATETIME_NOW_METHODDEF    \
-    {"now", (PyCFunction)datetime_datetime_now, METH_FASTCALL|METH_CLASS, datetime_datetime_now__doc__},
+    {"now", (PyCFunction)datetime_datetime_now, METH_FASTCALL|METH_KEYWORDS|METH_CLASS, datetime_datetime_now__doc__},
 
 static PyObject *
 datetime_datetime_now_impl(PyTypeObject *type, PyObject *tz);
@@ -36,4 +36,4 @@
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=ff78f2f51687e9a9 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=93cb014e47dae4b3 input=a9049054013a1b77]*/