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

Co-authored-by: Felipe <felipe.nospam.ochoa@gmail.com>

"sychronization" -> "synchronization"

PyUnicode_AsUnicodeAndSize() -> PyUnicode_AsWideChar()

bpo-30485: Change the prefix for defining the default namespace in ElementPath from None to '' since there is existing code that uses that and it's more convenient to have an all-string-keys dict (e.g. when sorting items etc.). (#12860)

# [bpo-36651](https://bugs.python.org/issue36651): Fixed Asyncio Event Loop documentation inconsistency  

In the documentation for the call_later and the call_at methods there is a note which says that the delay cannot be longer than a day, but both methods have a note saying that this limitation was removed in Python 3.8
Here I fixed this issue by removing the pre-exising note and added a versionchanged. 

To test my changes I have rebuilt the documentation with ```make html```. I did not have any errors and the effected page displayed correctly on a browser.



https://bugs.python.org/issue36651

Add a new _testinternalcapi module to test the internal C API.

Move _Py_GetConfigsAsDict() function to the internal C API:
_testembed now uses _testinternalcapi to access the function.

This paragraph doesn't seem to be a part of code, but merged into previous code block.

Change PyAPI_FUNC(type), PyAPI_DATA(type) and PyMODINIT_FUNC macros
of pyport.h when Py_BUILD_CORE_MODULE is defined.

The Py_BUILD_CORE_MODULE define must be now be used to build a C
extension as a dynamic library accessing Python internals: export the
PyInit_xxx() function in DLL exports on Windows.

Changes:

* Py_BUILD_CORE_BUILTIN and Py_BUILD_CORE_MODULE now imply
  Py_BUILD_CORE directy in pyport.h.
* ceval.c compilation now fails with an error if Py_BUILD_CORE is not
  defined, just to ensure that Python is build with the correct
  defines.
* setup.py now compiles _pickle.c with Py_BUILD_CORE_MODULE define.
* setup.py compiles _json.c with Py_BUILD_CORE_MODULE define, rather
  than Py_BUILD_CORE_BUILTIN define
* PCbuild/pythoncore.vcxproj: Add Py_BUILD_CORE_BUILTIN define.

Fix Python Initialization code on FreeBSD to detect properly when
stdin file descriptor (fd 0) is invalid.

On FreeBSD, fstat() must be used to check if stdin (fd 0) is valid.
dup(0) doesn't fail if stdin is invalid in some cases.