stdlib: add companion objects for Enum and String

runtime/src/main/kotlin/kotlin/Enum.kt

@@ -6,6 +6,8 @@ package kotlin
  * information on enum classes.
  */
 public abstract class Enum<E: Enum<E>>(public val name: String, public val ordinal: Int): Comparable<E> {
+    public companion object {
+    }
 
     public override final fun compareTo(other: E): Int { return ordinal - other.ordinal }
 

runtime/src/main/kotlin/kotlin/String.kt

@@ -3,6 +3,9 @@ package kotlin
 
 @ExportTypeInfo("theStringTypeInfo")
 public final class String : Comparable<String>, CharSequence {
+    public companion object {
+    }
+
     @SymbolName("Kotlin_String_hashCode")
     external public override fun hashCode(): Int