[Wasm][Stdlib] Reuse K/N collections and StringBuilder

libraries/stdlib/wasm/stubs/native/concurrent.kt

@@ -0,0 +1,11 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.native.concurrent
+
+// Only for compatibility with shared K/N stdlib code
+
+internal val Any?.isFrozen
+    inline get() = false

libraries/stdlib/wasm/stubs/native/internal.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.native.internal
+
+// Only for compatibility with shared K/N stdlib code
+
+internal interface KonanSet<out E> : Set<E> {
+    fun getElement(element: @UnsafeVariance E): E?
+}
+
+@Target(AnnotationTarget.CLASS)
+@Retention(AnnotationRetention.SOURCE)
+internal annotation class CanBePrecreated