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.

Rename Include/internal/ headers:

* pycore_hash.h -> pycore_pyhash.h
* pycore_lifecycle.h -> pycore_pylifecycle.h
* pycore_mem.h -> pycore_pymem.h
* pycore_state.h -> pycore_pystate.h

Add missing headers to Makefile.pre.in and PCbuild:

* pycore_condvar.h.
* pycore_hamt.h
* pycore_pyhash.h