Prohibit to override equals/hashCode in enums

#KT-5721 Fixed

compiler/testData/diagnostics/tests/enum/overrideFinalEnumMethods.kt

@@ -0,0 +1,9 @@
+enum class E {
+    ENTRY;
+
+    <!OVERRIDING_FINAL_MEMBER!>override<!> fun name(): String = "lol"
+    <!OVERRIDING_FINAL_MEMBER!>override<!> fun ordinal(): Int = 0
+
+    <!OVERRIDING_FINAL_MEMBER!>override<!> fun equals(other: Any?) = true
+    <!OVERRIDING_FINAL_MEMBER!>override<!> fun hashCode() = -1
+}

compiler/testData/diagnostics/tests/enum/overrideFinalEnumMethods.txt

@@ -0,0 +1,32 @@
+package 
+
+internal final enum class E : kotlin.Enum<E> {
+    private constructor E()
+    public open override /*1*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ fun name(): kotlin.String
+    public open override /*1*/ fun ordinal(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    
+    public enum entry ENTRY : E {
+        private constructor ENTRY()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun name(): kotlin.String
+        public open override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        
+        public class object <class-object-for-ENTRY> : E.ENTRY {
+            private constructor <class-object-for-ENTRY>()
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun name(): kotlin.String
+            public open override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
+    }
+    
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): E
+    public final /*synthesized*/ fun values(): kotlin.Array<E>
+}

compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java

@@ -3907,6 +3907,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
             
+            @TestMetadata("overrideFinalEnumMethods.kt")
+            public void testOverrideFinalEnumMethods() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/enum/overrideFinalEnumMethods.kt");
+                doTest(fileName);
+            }
+            
             @TestMetadata("starImportNestedClassAndEntries.kt")
             public void testStarImportNestedClassAndEntries() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/enum/starImportNestedClassAndEntries.kt");

core/builtins/native/kotlin/Enum.kt

@@ -16,7 +16,10 @@
 
 package kotlin
 
-public abstract class Enum<E: Enum<E>>(name: String, ordinal: Int) {
+public abstract class Enum<E : Enum<E>>(name: String, ordinal: Int) {
-  public final fun name()    : String
+    public final fun name(): String
-  public final fun ordinal() : Int
+    public final fun ordinal(): Int
+
+    public override final fun equals(other: Any?): Boolean
+    public override final fun hashCode(): Int
 }