Make scala corpus cross buildable with 2.12 and 2.13 again (part 2)

Author: retronym

corpus/scala/df29ebb/library/scala/collection/SeqFactory.scala

@@ -0,0 +1,6 @@
+package scala.collection
+
+object SeqFactory {
+  // dummy to avoid FatalError when the 2.13.x pattern matcher looks up this symbol.
+  final class UnapplySeqWrapper
+}