Fix Erasure.Boxing isBox and isUnbox

Box& unbox methods are defined in companion objects.

Author: DarkDimius

src/dotty/tools/dotc/transform/Erasure.scala

@@ -111,10 +111,10 @@ object Erasure extends TypeTestsCasts{
   object Boxing {
 
     def isUnbox(sym: Symbol)(implicit ctx: Context) =
-      sym.name == nme.unbox && (defn.ScalaBoxedClasses contains sym.owner)
+      sym.name == nme.unbox && (defn.ScalaBoxedClasses contains sym.owner.linkedClass)
 
     def isBox(sym: Symbol)(implicit ctx: Context) =
-      sym.name == nme.box && (defn.ScalaValueClasses contains sym.owner)
+      sym.name == nme.box && (defn.ScalaValueClasses contains sym.owner.linkedClass)
 
     def boxMethod(cls: ClassSymbol)(implicit ctx: Context) =
       cls.linkedClass.info.member(nme.box).symbol