bpo-30125: disable faulthandler in ctypes test_SEH

[vstinner]

Disable faulthandler to run test_SEH() of test_ctypes to prevent the
following log with a traceback:

Windows fatal exception: access violation

[mention-bot]

@Haypo, thanks for your PR! By analyzing the history of the files in this pull request, we identified @zware, @theller and @serhiy-storchaka to be potential reviewers.

[zware]

LGTM, but when could faulthandler be missing? I think you could use support.import_module to simplify things and still have protection from missing faulthandler if it's needed.

[vstinner]

Wait... faulthandler.disable() is broken on Windows: I simply forgot to implement RemoveVectoredExceptionHandler()! I will write a second PR.

[vstinner]

LGTM, but when could faulthandler be missing?

Other Python implementations may implement ctypes but not faulthandler.

Note: PyPy implements faulthandler, but I don't know if they implemented the Windows exception handler.

[vstinner]

See #1240 for the faulthandler.disable() fix.

[vstinner]

Oh, the first run of test_ctypes using -W failed:

======================================================================
ERROR: test_SEH (ctypes.test.test_win32.FunctionCallTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\ctypes\test\test_win32.py", line 64, in test_SEH
    faulthandler.enable()
io.UnsupportedOperation: fileno
----------------------------------------------------------------------
Ran 465 tests in 0.922s

But the second run without -W succeeded.

I fixed my change to call enable() with file=sys.stderr.fileno() instead. I should now work in all cases. I also fixed enable() call: pass all_threads=True.

Since the code became more complex than expected, I moved it to a new helper in test.support.

I saw that test.support always import faulthandler, so I removed the try/except ImportError.