When the line is uncommented, the equals character causes it to be incorrectly interpreted
as a macro definition by makesetup.  This results in invalid Makefile output.

The expat code only requires XML_POOR_ENTROPY to be defined; the value is unnecessary.

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.

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.

locale.localeconv() now sets temporarily the LC_CTYPE locale to the
LC_MONETARY locale if the two locales are different and monetary
strings are non-ASCII. This temporary change affects other threads.

Changes:

* locale.localeconv() can now set LC_CTYPE to LC_MONETARY to decode
  monetary fields.
* Add LocaleInfo.grouping_buffer: copy localeconv() grouping string
  since it can be replaced anytime if a different thread calls
  localeconv().
* _Py_GetLocaleconvNumeric() now requires a "struct lconv *"
  structure, so locale.localeconv() now longer calls localeconv()
  twice. Moreover, the function now requires all arguments to be
  non-NULL.
* Rename STATIC_LOCALE_INFO_INIT to LocaleInfo_STATIC_INIT.
* Move _Py_GetLocaleconvNumeric() definition from fileutils.h
  to pycore_fileutils.h. pycore_fileutils.h now includes locale.h.
* The _locale module is now built with Py_BUILD_CORE defined.

* All internal header files now require Py_BUILD_CORE or
  Py_BUILD_CORE_BUILTIN to be defined.
* _json.c is now compiled with Py_BUILD_CORE_BUILTIN to access
  pycore_accu.h header.
* Add an example to Modules/Setup to show how to build _json
  as a built-in module; it requires non trivial compiler options.

This could cause compile errors on macOS or other platforms.

* Rename Include/internal/ header files:

  * pyatomic.h -> pycore_atomic.h
  * ceval.h -> pycore_ceval.h
  * condvar.h -> pycore_condvar.h
  * context.h -> pycore_context.h
  * pygetopt.h -> pycore_getopt.h
  * gil.h -> pycore_gil.h
  * hamt.h -> pycore_hamt.h
  * hash.h -> pycore_hash.h
  * mem.h -> pycore_mem.h
  * pystate.h -> pycore_state.h
  * warnings.h -> pycore_warnings.h

* PCbuild project, Makefile.pre.in, Modules/Setup: add the
  Include/internal/ directory to the search paths of header files.
* Update includes. For example, replace #include "internal/mem.h"
  with #include "pycore_mem.h".

_PyTraceMalloc_NewReference() is now called by _Py_NewReference(), so
move its definition to object.h. Moreover, define it even if
Py_LIMITED_API is defined, since _Py_NewReference() is also exposed
even if Py_LIMITED_API is defined.