On Unix, C extensions are no longer linked to libpython.

It is now possible to load a C extension built using a shared library
Python with a statically linked Python.

When Python is embedded, libpython must not be loaded with
RTLD_LOCAL, but RTLD_GLOBAL instead. Previously, using RTLD_LOCAL, it
was already not possible to load C extensions which were not linked
to libpython, like C extensions of the standard library built by the
"*shared*" section of Modules/Setup.

distutils, python-config and python-config.py have been modified.

Document that subprocess.Popen no longer raise an exception on error
like missing program on very specific platforms when using
os.posix_spawn() is used.

bpo-28552, bpo-7774: Fix distutils.sysconfig if sys.executable is
None or an empty string: use os.getcwd() to initialize project_base.

Fix also the distutils build command: don't use sys.executable if
it's evaluated as false (None or empty string).

Fix Py_DEBUG constant: check for sys.gettotalrefcount attribute
rather than sys.getobjects.

Update also SpecialBuilds.txt documentation.

Release build and debug build are now ABI compatible: the Py_DEBUG
define no longer implies Py_TRACE_REFS define which introduces the
only ABI incompatibility.

A new "./configure --with-trace-refs" build option is now required to
get Py_TRACE_REFS define which adds sys.getobjects() function and
PYTHONDUMPREFS environment variable.

Changes:

* Add ./configure --with-trace-refs
* Py_DEBUG no longer implies Py_TRACE_REFS

Add myself to the codeowners file as I would like to
be automatically added as a reviewer for PRs that touch
that component.

Fix the multiprocessing.semaphore_tracker so it is reused by child processes.

This is meant as a stub, during the PyCon sprints we can iterate.

Py_InitializeEx() now uses a runtime variable passed to subfunctions,
rather than working directly on the global variable _PyRuntime.

Add 'runtime' parameter to _PyCoreConfig_Write(), _PySys_Create(),
_PySys_InitMain(), _PyGILState_Init(),
emit_stderr_warning_for_legacy_locale() and other subfunctions.

* Add a 'runtime' variable to Py_FinalizeEx() rather than working
  directly on the global variable _PyRuntime
* Add a 'runtime' parameter to _PyGC_Fini(), _PyGILState_Fini()
  and call_ll_exitfuncs()

* document relative imports

* 📜🤖 Added by blurb_it.

* fix indentation error

* remove indentation

* Document relative imports

* Document relative imports

* remove from ...package

* Document relative imports

* remove trailing space

* Document relative imports

* Document relative imports

The PyOS_AfterFork_Child() function now pass a 'runtime' parameter to
subfunctions.

* Fix _PyRuntimeState_ReInitThreads(): use the correct memory allocator
* Add runtime parameter to _PyRuntimeState_ReInitThreads(),
  _PyGILState_Reinit() and _PyInterpreterState_DeleteExceptMain()
* Move _PyGILState_Reinit() to the internal C API.

* Add 'runtime' parameter to _PyThreadState_Init()
* Add 'gilstate' parameter to _PyGILState_NoteThreadState()
* Move _PyThreadState_Init() and _PyThreadState_DeleteExcept()
   to the internal C API.

"./configure --with-pymalloc" no longer adds the "m" flag to SOABI
(sys.implementation.cache_tag).

Enabling or disabling pymalloc has no impact on the ABI.

Change test_time.test_monotonic() to test only the lower bound of elapsed time
after a sleep command rather than the upper bound. This prevents unnecessary
test failures on slow buildbots. Patch by Victor Stinner.

xlc compiler doesn't support "-D define" flag only "-Ddefine".