Python/frozenmain.c should use pre-initialization and be adapted for _PyCoreConfig. Py_FrozenMain() reimplements some features which are now implemented by _Py_InitializeFromConfig():

* disable C streams (stdin, stdout, stderr) buffering
* decode argv using Py_DecodeLocale()
* set the program name (call Py_SetProgramName())
* set sys.argv
* reimplement the REPL

It seems like it could use _Py_RunMain(), but I'm not sure.

Another file which should maybe also be updated to PEP 587, PC/bdist_wininst/install.c:

static int compile_filelist(HINSTANCE hPython, BOOL optimize_flag)
{
    DECLPROC(hPython, void, Py_Initialize, (void));
    DECLPROC(hPython, void, Py_SetProgramName, (wchar_t *));
    DECLPROC(hPython, void, Py_Finalize, (void));
    DECLPROC(hPython, int, PyRun_SimpleString, (char *));
    DECLPROC(hPython, PyObject *, PySys_GetObject, (char *));
    DECLVAR(hPython, int, Py_OptimizeFlag);

    int errors = 0;
    struct tagFile *p = file_list;

    if (!p)
        return 0;

    if (!Py_Initialize || !Py_SetProgramName || !Py_Finalize)
        return -1;

    if (!PyRun_SimpleString || !PySys_GetObject || !Py_OptimizeFlag)
        return -1;

    *Py_OptimizeFlag = optimize_flag ? 1 : 0;
    Py_SetProgramName(wmodulename);
    Py_Initialize();

    errors += do_compile_files(PyRun_SimpleString, optimize_flag);
    Py_Finalize();

    return errors;
}

Fixed by bpo-44131.

> Another file which should maybe also be updated to PEP 587, PC/bdist_wininst/install.c

PC/bdist_wininst/ has been removed in the meanwhile.