Set JavDefined flag for Object

Also, make all synthetic classes produced in Definitions Open.

Author: odersky

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -43,10 +43,10 @@ class Definitions {
     ctx.newSymbol(owner, name, flags | Permanent, info)
 
   private def newClassSymbol(owner: Symbol, name: TypeName, flags: FlagSet, infoFn: ClassSymbol => Type) =
-    ctx.newClassSymbol(owner, name, flags | Permanent | NoInits, infoFn)
+    ctx.newClassSymbol(owner, name, flags | Permanent | NoInits | Open, infoFn)
 
   private def enterCompleteClassSymbol(owner: Symbol, name: TypeName, flags: FlagSet, parents: List[TypeRef], decls: Scope = newScope) =
-    ctx.newCompleteClassSymbol(owner, name, flags | Permanent | NoInits, parents, decls).entered
+    ctx.newCompleteClassSymbol(owner, name, flags | Permanent | NoInits | Open, parents, decls).entered
 
   private def enterTypeField(cls: ClassSymbol, name: TypeName, flags: FlagSet, scope: MutableScope) =
     scope.enter(newSymbol(cls, name, flags, TypeBounds.empty))
@@ -279,7 +279,7 @@ class Definitions {
     val cls = ctx.requiredClass("java.lang.Object")
     assert(!cls.isCompleted, "race for completing java.lang.Object")
     cls.info = ClassInfo(cls.owner.thisType, cls, AnyClass.typeRef :: Nil, newScope)
-    cls.setFlag(NoInits)
+    cls.setFlag(NoInits | JavaDefined)
 
     // The companion object doesn't really exist, so it needs to be marked as
     // absent. Here we need to set it before completing attempt to load Object's