[K/N] Fix possible data races found by thread sanitizer

compiler/testData/codegen/box/topLevelInitializtion/concurrent.kt

@@ -0,0 +1,41 @@
+// TARGET_BACKEND: NATIVE
+
+// FILE: 1.kt
+
+val O = if (true) "O" else "F" // to avoid const init
+val K = if (true) "K" else "A" // to avoid const init
+
+// FILE: main.kt
+
+import kotlin.native.concurrent.*
+
+val sem = AtomicInt(0)
+
+fun box() : String {
+    val w1 = Worker.start()
+    val w2 = Worker.start()
+    val f1 = w1.execute(
+        mode = TransferMode.SAFE,
+        { },
+        {
+            sem.increment();
+            while (sem.value != 3) {}
+            O
+        }
+    )
+    val f2 = w2.execute(
+        mode = TransferMode.SAFE,
+        { },
+        {
+            sem.increment();
+            while (sem.value != 3) {}
+            K
+        }
+    )
+    while (sem.value != 2) {}
+    sem.value = 3
+    val result = f1.result + f2.result
+    w1.requestTermination().result
+    w2.requestTermination().result
+    return result
+}