Generate values()/valueOf() even for empty enums

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

@@ -0,0 +1,13 @@
+enum class Empty
+
+fun box(): String {
+    if (Empty.values().size != 0) return "Fail: ${Empty.values()}"
+
+    try {
+        val found = Empty.valueOf("nonExistentEntry")
+        return "Fail: $found"
+    }
+    catch (e: Exception) {
+        return "OK"
+    }
+}