bpo-42591: Export missing Py_FrozenMain() symbol (GH-23730)

Export the Py_FrozenMain() function: fix a Python 3.9.0 regression.
Python 3.9 uses -fvisibility=hidden and the function was not exported
explicitly and so not exported.

Add also Py_FrozenMain to the stable ABI on Windows.

Author: vstinner

Include/pylifecycle.h

@@ -32,6 +32,8 @@ PyAPI_FUNC(void) _Py_NO_RETURN Py_Exit(int);
 /* Bootstrap __main__ (defined in Modules/main.c) */
 PyAPI_FUNC(int) Py_Main(int argc, wchar_t **argv);
 
+PyAPI_FUNC(int) Py_FrozenMain(int argc, char **argv);
+
 PyAPI_FUNC(int) Py_BytesMain(int argc, char **argv);
 
 /* In pathconfig.c */

Misc/NEWS.d/next/C API/2020-12-10-10-43-03.bpo-42591.CXNY8G.rst

@@ -0,0 +1,3 @@
+Export the :c:func:`Py_FrozenMain` function: fix a Python 3.9.0 regression.
+Python 3.9 uses ``-fvisibility=hidden`` and the function was not exported
+explicitly and so not exported.

PC/python3dll.c

@@ -49,6 +49,7 @@ EXPORT_FUNC(Py_Exit)
 EXPORT_FUNC(Py_FatalError)
 EXPORT_FUNC(Py_Finalize)
 EXPORT_FUNC(Py_FinalizeEx)
+EXPORT_FUNC(Py_FrozenMain)
 EXPORT_FUNC(Py_GenericAlias)
 EXPORT_FUNC(Py_GenericAliasType)
 EXPORT_FUNC(Py_GetArgcArgv)