Fix Ycheck after recheck problem

Needs to signal that basetypes are changed

Author: odersky

compiler/src/dotty/tools/dotc/transform/Recheck.scala

@@ -25,6 +25,7 @@ abstract class Recheck extends Phase, IdentityDenotTransformer:
   def preRecheckPhase = this.prev.asInstanceOf[PreRecheck]
 
   override def isEnabled(using Context) = ctx.settings.Yrecheck.value
+  override def changesBaseTypes: Boolean = true
 
   def run(using Context): Unit =
     val unit = ctx.compilationUnit

compiler/test/dotc/pos-test-recheck.exludes

@@ -4,7 +4,3 @@ i6635a.scala
 # Cannot handle closures with skolem types
 i6199b.scala
 i6199c.scala
-
-# Skolemized type fails -Ycheck after recheck (NamedType caching problem?)
-i583a.scala
-