test_embed: test_thread_state_ensure() failed on "AMD64 Debian root 3.15" buildbot

AMD64 Debian root 3.15: https://buildbot.python.org/#/builders/2019/builds/85

FAIL: test_thread_state_ensure (test.test_embed.AuditingTests.test_thread_state_ensure)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/root/buildarea/3.15.angelico-debian-amd64/build/Lib/test/test_embed.py", line 2000, in test_thread_state_ensure
    self.run_embedded_interpreter("test_thread_state_ensure")
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/buildarea/3.15.angelico-debian-amd64/build/Lib/test/test_embed.py", line 138, in run_embedded_interpreter
    self.assertEqual(p.returncode, returncode,
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
                     "bad returncode %d, stderr is %r" %
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     (p.returncode, err))
                     ^^^^^^^^^^^^^^^^^^^^
AssertionError: -6 != 0 : bad returncode -6, stderr is "_testembed: ./Programs/_testembed.c:2736: test_thread_state_ensure: Assertion `_Py_atomic_load_int(&data.done) == 1' failed.\n"

Stdout:
--- ['/root/buildarea/3.15.angelico-debian-amd64/build/Programs/_testembed', 'test_thread_state_ensure'] failed ---
stdout:

stderr:
_testembed: ./Programs/_testembed.c:2736: test_thread_state_ensure: Assertion `_Py_atomic_load_int(&data.done) == 1' failed.

cc @ZeroIntensity

Comienza con Lib/test/test_embed.py, especialmente AuditingTests.test_thread_state_ensure y run_embedded_interpreter, y después inspecciona Programs/_testembed.c en test_thread_state_ensure alrededor de la aserción que falla. Reproduce el fallo en la configuración del buildbot AMD64 Debian y determina qué se necesita para que la prueba termine con data.done igual a 1 y devuelva el código de retorno 0.