Under some conditions the earlier fix for bpo-18075, "Infinite recursion
tests triggering a segfault on Mac OS X", now causes failures on macOS
when attempting to change stack limit with resource.setrlimit
resource.RLIMIT_STACK, like regrtest does when running the test suite.
The reverted change had specified a non-default stack size when linking
the python executable on macOS.  As of macOS 10.14.4, the previous
code causes a hard failure when running tests, although similar
failures had been seen under some conditions under some earlier
systems.  For now, revert the original change and resume using
the default stack size when linking the interpreter.

This commit implements the first version of date.fromisocalendar, the
inverse function for date.isocalendar.

This commit contains the implementation of PEP570: Python positional-only parameters.

* Update Grammar/Grammar with new typedarglist and varargslist

* Regenerate grammar files

* Update and regenerate AST related files

* Update code object

* Update marshal.c

* Update compiler and symtable

* Regenerate importlib files

* Update callable objects

* Implement positional-only args logic in ceval.c

* Regenerate frozen data

* Update standard library to account for positional-only args

* Add test file for positional-only args

* Update other test files to account for positional-only args

* Add News entry

* Update inspect module and related tests

This reverts commit b36e5d62.

* Add _PyEval_FiniThreads2(). _PyEval_FiniThreads() now only clears
  the pending lock, whereas _PyEval_FiniThreads2() destroys the GIL.
* pymain_free() now calls _PyEval_FiniThreads2().
* Py_FinalizeEx() now calls _PyEval_FiniThreads().

PyEval_AcquireLock() and PyEval_AcquireThread() now
terminate the current thread if called while the interpreter is
finalizing, making them consistent with PyEval_RestoreThread(),
Py_END_ALLOW_THREADS, and PyGILState_Ensure().

https://bugs.python.org/issue36745

* Fix typo in test_cyclic_gc subtest
* Improve test coverage for xml.etree.ElementTree

In the process of converting the date.fromtimestamp function to use
argument clinic in GH-8535, the C API for PyDate_FromTimestamp was
inadvertently changed to expect a timestamp object rather than an
argument tuple.

This PR fixes this backwards-incompatible change by adding a new wrapper
function for the C API function that unwraps the argument tuple and
passes it to the underlying function.

This PR also adds tests for both PyDate_FromTimestamp and
PyDateTime_FromTimestamp to prevent any further regressions.

The new markup is currently ignored by IDLE's tk doc display.

Py_TRACE_REFS ABI is incompatible with release and debug (Py_DEBUG)
ABI.

Misc/python-config.sh lives in the build directory, not in the source
directory.

Add PYTHONPATH=$(srcdir) to run $(PYTHON_FOR_REGEN) -m Parser.pgen,
so it's possible to build Python from a different directory.

Add _Py_INIT_HAS_EXITCODE() macro.

Regrtest.finalize() now closes explicitly the WindowsLoadTracker
instance.

Properly handle a test which fail but then pass.

Add test_rerun_success() unit test.

regrtest now always detects uncollectable objects. Previously, the
check was only enabled by --findleaks. The check now also works with
-jN/--multiprocess N.

--findleaks becomes a deprecated alias to --fail-env-changed.

Rewrite run_tests_multiprocess() function as a new MultiprocessRunner
class with multiple methods to better report errors and stop
immediately when needed.

Changes:

* Worker processes are now killed immediately if tests are
  interrupted or if a test does crash (CHILD_ERROR): worker
  processes are killed.
* Rewrite how errors in a worker thread are reported to
  the main thread. No longer ignore BaseException or parsing errors
  silently.
* Remove 'finished' variable: use worker.is_alive() instead
* Always compute omitted tests. Add Regrtest.get_executed() method.

Py_FinalizeEx() now clears _PyRuntime.warnings variables and
_PyRuntime.exitfuncs.

Changes:

* Add _PyWarnings_Fini(): called by Py_FinalizeEx()
* call_ll_exitfuncs() now clears _PyRuntime.exitfuncs while iterating
  on it (on backward order).

_PyThreadState_Delete() has no return value.

* Add TestResult and MultiprocessResult types to ensure that results
  always have the same fields.
* runtest() now handles KeyboardInterrupt
* accumulate_result() and format_test_result() now takes a TestResult
* cleanup_test_droppings() is now called by runtest() and mark the
  test as ENV_CHANGED if the test leaks support.TESTFN file.
* runtest() now includes code "around" the test in the test timing
* Add print_warning() in test.libregrtest.utils to standardize how
  libregrtest logs warnings to ease parsing the test output.
* support.unload() is now called with abstest rather than test_name
* Rename 'test' variable/parameter to 'test_name'
* dash_R(): remove unused the_module parameter
* Remove unused imports

Add 'state' or 'runtime' parameter to functions in gcmodule.c to
avoid to rely directly on the global variable _PyRuntime.

Add 'gilstate', 'runtime' or 'xidregistry' parameter to many
functions on pystate.c to avoid lying on _PyRuntime global.

In debug build, import now also looks for C extensions compiled in
release mode and for C extensions compiled in the stable ABI.