fix(libc): run thread-local destructors

Why: Thread-atexit registrations were discarded, leaving objects alive after their guest TLS storage was released.

What: Store registrations per host thread and run them in LIFO order before pthread keys and guest TLS are destroyed.

Why safe: Only callbacks registered on the exiting thread run, once, before existing teardown continues.

src/kernel/pthread.cpp

@@ -65,6 +65,10 @@
 
 namespace Libs {
 
+namespace LibcInternalExt {
+void RunThreadAtexitDestructors();
+} // namespace LibcInternalExt
+
 namespace LibKernel {
 
 LIB_NAME("libkernel", "libkernel");
@@ -3347,6 +3351,8 @@ int PthreadGetCurrentPriorityForKernel() {
 static void CleanupThread(void* arg) {
 	auto* thread = static_cast<Pthread>(arg);
 
+	LibcInternalExt::RunThreadAtexitDestructors();
+
 	auto thread_dtors = g_pthread_context->GetThreadDtors();
 
 	if (thread_dtors != nullptr) {