Fix java enum flag

Previously the flag is not set properly

Author: liufengyun

compiler/src/dotty/tools/dotc/core/classfile/ClassfileConstants.scala

@@ -362,6 +362,7 @@ object ClassfileConstants {
       res = addFlag(res, nflags & JAVA_ACC_FINAL)
       res = addFlag(res, nflags & JAVA_ACC_SYNTHETIC)
       res = addFlag(res, nflags & JAVA_ACC_STATIC)
+      res = addFlag(res, nflags & JAVA_ACC_ENUM)
       res = addFlag(res, nflags & JAVA_ACC_ABSTRACT)
       res = addFlag(res, nflags & JAVA_ACC_INTERFACE)
       res

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

@@ -120,6 +120,9 @@ object TypeTestsCasts {
       maximizeType(P1, span, fromScala2x = false)
 
       val res = P1 <:< P
+
+      debug.println(TypeComparer.explained(P1 <:< P))
+
       debug.println("P1 : " + P1.show)
       debug.println("P1 <:< P = " + res)