kernel: name guest threads on the host (#1106)

PthreadCreate carries a guest thread name, but RunThread never handed it to
the host, so every guest thread showed up as the same generic host thread
name in core dumps, perf samples and htop.

Call pthread_setname_np() on Linux so host-side diagnostics can attribute
work to the guest thread that caused it.

src/kernel/pthread.cpp

@@ -3200,6 +3200,11 @@ static void* RunThread(void* arg) {
 	os_thread_id = GetHostThreadId();
 #endif
 	thread->host_thread_id = os_thread_id;
+#if KYTY_PLATFORM == KYTY_PLATFORM_LINUX
+	if (!thread->name.empty()) {
+		pthread_setname_np(pthread_self(), thread->name.substr(0, 15).c_str());
+	}
+#endif
 
 	LOGF("\tPthread run begin: %s, id = %d, os_thread_id = %" PRIu64 ", entry = 0x%016" PRIx64
 	     ", arg = 0x%016" PRIx64 ", stack_addr = 0x%016" PRIx64 ", stack_size = %" PRIu64 "\n",