Test results against patched libffi in Modules/_ctypes:

shell@ASUS_Z00E_2:/data/local/tmp $ python3.6 -m test.test_ctypes              
...................................................................s......s..............s....................ssssssssssssssssssssss..................................ssssssssssssssssssssssssssss.s...sssOpenGL libraries:
         ('GL', None)
         ('GLU', None)
         ('gle', None)
sss...........................s.s............s.........libc_name is None
ss.sssss...s...s...........s....s..................................................................s.................................sssss..ss..........................s....................ssFsssssss
======================================================================
FAIL: test_struct_by_value (ctypes.test.test_win32.Structures)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/data/local/tmp/python3/lib/python3.6/ctypes/test/test_win32.py", line 133, in test_struct_by_value
    self.assertEqual(ret.left, left.value)
AssertionError: -200 != 10

----------------------------------------------------------------------
Ran 456 tests in 1.970s

FAILED (failures=1, skipped=92)

A failure occurs with libffi 3.1 while all tests passes with libffi git-master. Issue23085 may be the solution.