Merge pull request #5850 from dotty-staging/fix-#4371-2

Fix #4371: Add regression tests

Author: liufengyun

tests/neg/i4371a.scala

@@ -0,0 +1,4 @@
+object App {
+  class Foo { type A = Boo#B } // error: illegal cyclic reference: alias App.Boo#B of type A refers back to the type itself
+  class Boo { type B = Foo#A }
+}

tests/neg/i4371b.scala

@@ -0,0 +1,3 @@
+object App {
+  type T[G[X] <: X, F[X] <: G[F[X]]] // error: Recursion limit exceeded. Maybe there is an illegal cyclic reference? ...
+}