Freeze objects by default, stdlib improvements. (#1743)

backend.native/tests/build.gradle

@@ -671,6 +671,12 @@ task freeze2(type: RunKonanTest) {
     source = "runtime/workers/freeze2.kt"
 }
 
+task freeze3(type: RunKonanTest) {
+    disabled = (project.testTarget == 'wasm32') // No exceptions on WASM.
+    goldValue = "OK\n"
+    source = "runtime/workers/freeze3.kt"
+}
+
 task atomic0(type: RunKonanTest) {
     disabled = (project.testTarget == 'wasm32') // Workers need pthreads.
     goldValue = "35\n" + "20\n" + "OK\n"

backend.native/tests/runtime/workers/freeze3.kt

@@ -0,0 +1,25 @@
+package runtime.workers.freeze3
+
+import kotlin.test.*
+
+import konan.worker.*
+
+object Immutable {
+    var x = 1
+}
+
+@konan.ThreadLocal
+object Mutable {
+    var x = 2
+}
+
+@Test fun runTest() {
+    assertEquals(1, Immutable.x)
+    assertFailsWith<InvalidMutabilityException> {
+        Immutable.x++
+    }
+    assertEquals(1, Immutable.x)
+    Mutable.x++
+    assertEquals(3, Mutable.x)
+    println("OK")
+}