Refchecks runs before resolveSuper: superAccessors not yet materialised.

Author: DarkDimius

src/dotty/tools/dotc/typer/RefChecks.scala

@@ -362,6 +362,7 @@ object RefChecks {
 
       def ignoreDeferred(member: SingleDenotation) =
         member.isType ||
+          member.symbol.is(SuperAccessor) || // not yet synthesized
           member.symbol.is(JavaDefined) && hasJavaErasedOverriding(member.symbol)
 
       // 2. Check that only abstract classes have deferred members