Make IvyXml.makeIvyXmlBefore private[sbt]

The publishLocalBin doesn't make an ivy.xml file. In order to add that
functionality, we need to make IvyXml.makeIvyXmlBefore available at the
private[sbt] level.

main/src/main/scala/sbt/internal/librarymanagement/IvyXml.scala

@@ -180,7 +180,7 @@ object IvyXml {
     </ivy-module>
   }
 
-  private def makeIvyXmlBefore[T](
+  private[sbt] def makeIvyXmlBefore[T](
       task: TaskKey[T],
       shadedConfigOpt: Option[Configuration]
   ): Setting[Task[T]] =