* calculate_path() rewritten in Modules/getpath.c and PC/getpathp.c
* Move global variables into a new PyPathConfig structure.
* calculate_path():

  * Split the huge calculate_path() function into subfunctions.
  * Add PyCalculatePath structure to pass data between subfunctions.
  * Document PyCalculatePath fields.
  * Move cleanup code into a new calculate_free() subfunction
  * calculate_init() now handles Py_DecodeLocale() failures properly
  * calculate_path() is now atomic: only replace PyPathConfig
    (path_config) at once on success.

* _Py_GetPythonHomeWithConfig() now returns an error on failure
* Add _Py_INIT_NO_MEMORY() helper: report a memory allocation failure
* Coding style fixes (PEP 7)

* Py_Main() now reads the PYTHONHOME environment variable
* Add _Py_GetPythonHomeWithConfig() private function
* Add _PyWarnings_InitWithConfig()
* init_filters() doesn't get the current core configuration from the
  current interpreter or Python thread anymore. Pass explicitly the
  configuration to _PyWarnings_InitWithConfig().
* _Py_InitializeCore() now fails on _PyWarnings_InitWithConfig()
  failure.
* Pass configuration as constant

Move _PyCoreConfig.module_search_path_env to _PyMainInterpreterConfig
structure.

Adds a simpler and faster alternative to ExitStack for handling
single optional context managers without having to change the
lexical structure of your code.

Patch mostly by Cheryl Sabella

Changes:

* Py_Main() initializes _PyCoreConfig.module_search_path_env from
  the PYTHONPATH environment variable.
* PyInterpreterState_New() now initializes core_config and config
  fields
* Compute sys.path a little bit ealier in
  _Py_InitializeMainInterpreter() and new_interpreter()
* Add _Py_GetPathWithConfig() private function.

* Optimize warnings.filterwarnings(). Replace re.compile('') with
  None to avoid the cost of calling a regex.match() method, whereas
  it always matchs.
* Optimize get_warnings_attr(): replace PyObject_GetAttrString() with
  _PyObject_GetAttrId().

Cleanup also create_filter():

* Use _Py_IDENTIFIER() to allow to cleanup strings at Python
  finalization
* Replace Py_FatalError() with a regular exceptions

* Rename support._match_test() to support.match_test(): make it
  public
* Remove support.match_tests global variable. It is replaced with a
  new support.set_match_tests() function, so match_test() doesn't
  have to check each time if patterns were modified.
* Rewrite match_test(): use different code paths depending on the
  kind of patterns for best performances.
Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>

Add one last minor clarification for idpattern

* should not be more verbose if the code is correct
* enabled checks can be "expensive"

Py_Main() now handles two more -X options:

* -X showrefcount: new _PyCoreConfig.show_ref_count field
* -X showalloccount: new _PyCoreConfig.show_alloc_count field

The developer mode (-X dev) now creates all default warnings filters
to order filters in the correct order to always show ResourceWarning
and make BytesWarning depend on the -b option.

Write a functional test to make sure that ResourceWarning is logged
twice at the same location in the developer mode.

Add a new 'dev_mode' field to _PyCoreConfig.

Modify subprocess._args_from_interpreter_flags() to handle -X dev
option.

Add also unit tests for test.support.args_from_interpreter_flags()
and test.support.optim_args_from_interpreter_flags().

When Python is build is debug mode (Py_DEBUG), DeprecationWarning,
PendingDeprecationWarning and ImportWarning warnings are now
displayed by default.

test_venv: run "-m pip" and "-m ensurepip._uninstall" with -W
ignore::DeprecationWarning since pip code is not part of Python.

The line number in correct when using the -x option: Py_Main() uses
ungetc() to not skip the first newline character.

The new -X dev command line option now also enables asyncio debug
mode.

Since f299abda
the remove_pyc() method no longer tries to
remove .pyo files.

`BUILD_MAP_UNPACK_WITH_CALL` was duplicated as the opcode for both var-positional and var-keyword arguments. The opcode for the former was updated as `BUILD_TUPLE_UNPACK_WITH_CALL`.

When there is a symlink in the directory path of the standard library.

* Run gzip with separate command line options (Android understands  '-f9' as the name of a file).
* Creation of a hard link is controled by SELinux on Android.

* Drop legacy SSL transport

* Drop unused import

* Fix Windows tests

* Drop never executed on Python 3.4+ code

Remove the following fields from tok_state structure which are now
used unused:

* altwarning: "Issue warning if alternate tabs don't match"
* alterror: "Issue error if alternate tabs don't match"
* alttabsize: "Alternate tab spacing"

Replace alttabsize variable with ALTTABSIZE define.

`kargs` -> `kwargs`

The log_rounds parameter for Blowfish has been replaced with the rounds parameter.

Add a new "developer mode": new "-X dev" command line option to
enable debug checks at runtime.

Changes:

* Add unit tests for -X dev
* test_cmd_line: replace test.support with support.
* Fix _PyRuntimeState_Fini(): Use the same memory allocator
   than _PyRuntimeState_Init().
* Fix _PyMem_GetDefaultRawAllocator()

in regular expressions.