fix: HasOrelse (DelabM _)

src/Lean/Delaborator.lean

@@ -95,6 +95,8 @@ protected def failure {α} : DelabM α := throw $ Exception.internal delabFailur
 instance : Alternative DelabM :=
 { orelse  := fun _ => Delaborator.orelse,
   failure := fun _ => Delaborator.failure }
+-- HACK: necessary since it would otherwise prefer the instance from MonadExcept
+instance {α} : HasOrelse (DelabM α) := alternativeHasOrelse _ _
 
 -- Macro scopes in the delaborator output are ultimately ignored by the pretty printer,
 -- so give a trivial implementation.