[IR] Enable -Xvalue-classes flag

Signed-off-by: Evgeniy.Zhelenskiy <Evgeniy.Zhelenskiy@jetbrains.com>

#KT-1179

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.kt

@@ -546,6 +546,12 @@ Also sets `-jvm-target` value equal to the selected JDK version"""
     )
     var oldInnerClassesLogic: Boolean by FreezableVar(false)
 
+    @Argument(
+        value = "-Xvalue-classes",
+        description = "Enable experimental value classes"
+    )
+    var valueClasses: Boolean by FreezableVar(false)
+
     override fun configureAnalysisFlags(collector: MessageCollector, languageVersion: LanguageVersion): MutableMap<AnalysisFlag<*>, Any> {
         val result = super.configureAnalysisFlags(collector, languageVersion)
         result[JvmAnalysisFlags.strictMetadataVersionSemantics] = strictMetadataVersionSemantics
@@ -581,6 +587,9 @@ Also sets `-jvm-target` value equal to the selected JDK version"""
             result[LanguageFeature.ForbidSuperDelegationToAbstractFakeOverride] = LanguageFeature.State.ENABLED
             result[LanguageFeature.AbstractClassMemberNotImplementedWithIntermediateAbstractClass] = LanguageFeature.State.ENABLED
         }
+        if (valueClasses) {
+            result[LanguageFeature.ValueClasses] = LanguageFeature.State.ENABLED
+        }
         return result
     }