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.
diff --git a/Include/pylifecycle.h b/Include/pylifecycle.h
index c5368b3..783fcb4 100644
--- a/Include/pylifecycle.h
+++ b/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 */