bpo-37547: add _PyObject_CallMethodOneArg (GH-14685)

diff --git a/Include/cpython/abstract.h b/Include/cpython/abstract.h
index e9a2319..d57aa54 100644
--- a/Include/cpython/abstract.h
+++ b/Include/cpython/abstract.h
@@ -163,6 +163,15 @@
            1 | PY_VECTORCALL_ARGUMENTS_OFFSET, NULL);
 }
 
+static inline PyObject *
+_PyObject_CallMethodOneArg(PyObject *self, PyObject *name, PyObject *arg)
+{
+    assert(arg != NULL);
+    PyObject *args[2] = {self, arg};
+    return _PyObject_VectorcallMethod(name, args,
+           2 | PY_VECTORCALL_ARGUMENTS_OFFSET, NULL);
+}
+
 /* Like PyObject_CallMethod(), but expect a _Py_Identifier*
    as the method name. */
 PyAPI_FUNC(PyObject *) _PyObject_CallMethodId(PyObject *obj,
@@ -198,6 +207,15 @@
            1 | PY_VECTORCALL_ARGUMENTS_OFFSET, NULL);
 }
 
+static inline PyObject *
+_PyObject_CallMethodIdOneArg(PyObject *self, _Py_Identifier *name, PyObject *arg)
+{
+    assert(arg != NULL);
+    PyObject *args[2] = {self, arg};
+    return _PyObject_VectorcallMethodId(name, args,
+           2 | PY_VECTORCALL_ARGUMENTS_OFFSET, NULL);
+}
+
 PyAPI_FUNC(int) _PyObject_HasLen(PyObject *o);
 
 /* Guess the size of object 'o' using len(o) or o.__length_hint__().