bpo-43795: Mark PyCodec_Unregister as a function, not data, in stable ABI (GH-25920)

(cherry picked from commit cf86996)

Co-authored-by: Petr Viktorin <[email protected]>

Author: miss-islington

Misc/NEWS.d/next/C API/2021-05-05-19-04-50.bpo-43795.9Ojj73.rst

@@ -0,0 +1,2 @@
+:c:func:`PyCodec_Unregister` is now properly exported as a function in the
+Windows Stable ABI DLL.

Misc/stable_abi.txt

@@ -2097,7 +2097,7 @@ function PyModule_AddObjectRef
     added 3.10
 data Py_FileSystemDefaultEncodeErrors
     added 3.10
-data PyCodec_Unregister
+function PyCodec_Unregister
     added 3.10
 function PyErr_SetInterruptEx
     added 3.10

PC/python3dll.c

@@ -156,6 +156,7 @@ EXPORT_FUNC(PyCodec_ReplaceErrors)
 EXPORT_FUNC(PyCodec_StreamReader)
 EXPORT_FUNC(PyCodec_StreamWriter)
 EXPORT_FUNC(PyCodec_StrictErrors)
+EXPORT_FUNC(PyCodec_Unregister)
 EXPORT_FUNC(PyCodec_XMLCharRefReplaceErrors)
 EXPORT_FUNC(PyComplex_FromDoubles)
 EXPORT_FUNC(PyComplex_ImagAsDouble)
@@ -734,7 +735,6 @@ EXPORT_DATA(PyCallIter_Type)
 EXPORT_DATA(PyCapsule_Type)
 EXPORT_DATA(PyCFunction_Type)
 EXPORT_DATA(PyClassMethodDescr_Type)
-EXPORT_DATA(PyCodec_Unregister)
 EXPORT_DATA(PyComplex_Type)
 EXPORT_DATA(PyDict_Type)
 EXPORT_DATA(PyDictItems_Type)