[K/N] Worker API improvements ^KT-52429

Merge-request: KT-MR-6898
Merged-by: Alexander Shabalin <Alexander.Shabalin@jetbrains.com>

kotlin-native/backend.native/tests/interop/workerSignals/workerSignals.cpp

@@ -0,0 +1,31 @@
+#include "workerSignals.h"
+
+#include <cassert>
+#include <pthread.h>
+#include <signal.h>
+
+namespace {
+
+int pendingValue = 0;
+thread_local int value = 0;
+
+void signalHandler(int signal) {
+    value = pendingValue;
+}
+
+} // namespace
+
+extern "C" void setupSignalHandler(void) {
+    signal(SIGUSR1, &signalHandler);
+}
+
+extern "C" void signalThread(uint64_t thread, int value) {
+    pendingValue = value;
+    auto t = reinterpret_cast<pthread_t>(thread);
+    auto result = pthread_kill(t, SIGUSR1);
+    assert(result == 0);
+}
+
+extern "C" int getValue(void) {
+    return value;
+}