Make PyDateTime_DELTA_*() macros in datetime.pxd available in Py2.

See https://github.com/cython/cython/pull/3616

Cython/Includes/cpython/datetime.pxd

@@ -5,6 +5,17 @@ cdef extern from "Python.h":
         pass
 
 cdef extern from "datetime.h":
+    """
+    #if PY_MAJOR_VERSION < 3 && !defined(PyDateTime_DELTA_GET_DAYS)
+    #define PyDateTime_DELTA_GET_DAYS(o)         (((PyDateTime_Delta*)o)->days)
+    #endif
+    #if PY_MAJOR_VERSION < 3 && !defined(PyDateTime_DELTA_GET_SECONDS)
+    #define PyDateTime_DELTA_GET_SECONDS(o)      (((PyDateTime_Delta*)o)->seconds)
+    #endif
+    #if PY_MAJOR_VERSION < 3 && !defined(PyDateTime_DELTA_GET_MICROSECONDS)
+    #define PyDateTime_DELTA_GET_MICROSECONDS(o)   (((PyDateTime_Delta*)o)->microseconds)
+    #endif
+    """
 
     ctypedef extern class datetime.date[object PyDateTime_Date]:
         pass

tests/run/datetime_pxd.pyx

@@ -12,6 +12,13 @@ from cpython.datetime cimport date_day, date_month, date_year
 from cpython.datetime cimport datetime_day, datetime_month, datetime_year
 from cpython.datetime cimport datetime_hour, datetime_minute, datetime_second, \
                               datetime_microsecond
+# These were added in Py3, make sure that their backport works.
+from cpython.datetime cimport (
+    timedelta as timedelta_ext_type,
+    PyDateTime_DELTA_GET_DAYS,
+    PyDateTime_DELTA_GET_SECONDS,
+    PyDateTime_DELTA_GET_MICROSECONDS,
+)
 
 import datetime as py_datetime
 
@@ -38,6 +45,22 @@ class FixedOffset(py_datetime.tzinfo):
     def dst(self, dt):
         return ZERO
 
+
+def do_timedelta_macros(timedelta_ext_type delta):
+    """
+    >>> delta = py_datetime.timedelta(days=13, hours=7, seconds=31, microseconds=993322)
+    >>> (delta.days, delta.seconds, delta.microseconds)
+    (13, 25231, 993322)
+    >>> do_timedelta_macros(delta)
+    (13, 25231, 993322)
+    """
+    return (
+        PyDateTime_DELTA_GET_DAYS(delta),
+        PyDateTime_DELTA_GET_SECONDS(delta),
+        PyDateTime_DELTA_GET_MICROSECONDS(delta),
+    )
+
+
 def do_date(int year, int month, int day):
     """
     >>> do_date(2012, 12, 31)