Fix #7991: don't set JavaDefined for Dotty Enum module class

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

@@ -200,12 +200,13 @@ class ClassfileParser(
         sym.markAbsent()
       }
 
-    // eager load java enum definitions for exhaustivity check of pattern match
+    // eager load enum definitions for exhaustivity check of pattern match
     if (isEnum) {
       instanceScope.toList.map(_.ensureCompleted())
       staticScope.toList.map(_.ensureCompleted())
-      classRoot.setFlag(Flags.JavaEnumTrait)
-      moduleRoot.setFlag(Flags.JavaEnumTrait)
+      val flag = if moduleRoot.is(Flags.JavaDefined) then Flags.JavaEnumTrait else Flags.Enum
+      classRoot.setFlag(flag)
+      moduleRoot.setFlag(flag)
     }
 
     result

tests/run/i7991.scala

@@ -0,0 +1,5 @@
+enum Num { case One }
+
+object Test extends App {
+  Num.One
+}

tests/run/i7991/Num_1.scala

@@ -0,0 +1 @@
+enum Num { case One }

tests/run/i7991/Test_2.scala

@@ -0,0 +1,3 @@
+object Test extends App {
+  Num.One
+}