bpo-43688: Support the limited C API in debug mode (GH-25131)

The limited C API is now supported if Python is built in debug mode
(if the Py_DEBUG macro is defined). In the limited C API, the
Py_INCREF() and Py_DECREF() functions are now implemented as opaque
function calls, rather than accessing directly the PyObject.ob_refcnt
member, if Python is built in debug mode and the Py_LIMITED_API macro
targets Python 3.10 or newer. It became possible to support the
limited C API in debug mode because the PyObject structure is the
same in release and debug mode since Python 3.8 (see bpo-36465).

The limited C API is still not supported in the --with-trace-refs
special build (Py_TRACE_REFS macro).
diff --git a/PC/python3dll.c b/PC/python3dll.c
index 1567ac1..b5735e8 100644
--- a/PC/python3dll.c
+++ b/PC/python3dll.c
@@ -36,6 +36,8 @@ EXPORT_FUNC(_PyTrash_deposit_object)
 EXPORT_FUNC(_PyTrash_destroy_chain)
 EXPORT_FUNC(_PyTrash_thread_deposit_object)
 EXPORT_FUNC(_PyTrash_thread_destroy_chain)
+EXPORT_FUNC(_Py_IncRef)
+EXPORT_FUNC(_Py_DecRef)
 EXPORT_FUNC(Py_AddPendingCall)
 EXPORT_FUNC(Py_AtExit)
 EXPORT_FUNC(Py_BuildValue)