Flushing sys.stdout and sys.stderr in Py_FatalError() can call again
Py_FatalError(). Add a reentrant flag to detect this case and just abort at the
second call.
sys.stderr
It should help to see exceptions when stderr if buffered: PyErr_Display() calls
sys.stderr.write(), it doesn't write into stderr file descriptor directly.
* Display the current Python stack if an exception was raised but the exception
has no traceback
* Disable faulthandler if an exception was raised (before it was only disabled
if no exception was raised)
* To display the current Python stack, call PyGILState_GetThisThreadState()
which works even if the GIL was released
Issue #26558: If Py_FatalError() is called without the GIL, don't try to print
the current exception, nor try to flush stdout and stderr: only dump the
traceback of Python threads.
Victor Stinner
Serhiy Storchaka
Zachary Ware
Nick Coghlan