[JVM IR] Use reference equality when comparing enums.

compiler/testData/codegen/box/enum/kt18731.kt

@@ -6,7 +6,7 @@ enum class Bar {
 fun isOne(i: Bar) = i == Bar.ONE
 
 fun box(): String {
-    return when (isOne(Bar.ONE) && !isOne(Bar.TWO)) {
+    return when (isOne(Bar.ONE) && !isOne(Bar.TWO) && Bar.ONE != Bar.TWO) {
         true -> "OK"
         else -> "Failure"
     }