bug#27598: MacOS: thread-signal-early fails

[Charles A. Roelli]

Following on from bug #25265 (make-thread crashes in OS X 10.6):

From:
$ nextstep/Emacs.app/Contents/MacOS/Emacs -Q -l ert -l 
test/src/thread-tests.el

M-x ert RET RET

Selector: t
Passed:  27
Failed:  1 (1 unexpected)
Skipped: 0
Total:   28/28

Started at:   2017-07-06 18:53:01+0200
Finished.
Finished at:  2017-07-06 18:53:02+0200

.F..........................

F thread-signal-early
    Test signaling a thread as soon as it is started by the OS.
    (ert-test-failed
     ((should-not
       (thread-alive-p thread))
      :form
      (thread-alive-p #<thread 0x1059645d8>)
      :value t))

It seems to only happen when input is arriving while running the test
(as when you keep on hitting RET after starting the tests).