internal/impl: handle extremely old messages

At some point in time, protoc-gen-go actually emitted an XXX_OneofFuncs
with a different signature. Adjust the logic for handling XXX_OneofFuncs
to not assume that the return arguments are in a specific order.

Change-Id: Idd9c09231c4129c655d4a635bb1ae094896a1ff4
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/226980
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/legacy_aberrant_test.go b/internal/impl/legacy_aberrant_test.go
index c51b0c7..905981a 100644
--- a/internal/impl/legacy_aberrant_test.go
+++ b/internal/impl/legacy_aberrant_test.go
@@ -86,7 +86,7 @@
 	return []protoiface.ExtensionRangeV1{{Start: 10, End: 100}}
 }
 
-func (m *AberrantMessage) XXX_OneofWrappers() []interface{} {
+func (m *AberrantMessage) XXX_OneofFuncs() []interface{} {
 	return []interface{}{
 		(*OneofBool)(nil),
 		(*OneofInt32)(nil),