Correct thread state update order (fixes Windows crashes).

runtime/vm/thread_interrupter_macos.cc

Index: runtime/vm/thread_interrupter_macos.cc
diff --git a/runtime/vm/thread_interrupter_macos.cc b/runtime/vm/thread_interrupter_macos.cc
index b5beeebedac7abef16c848fbcb6660b006d6dd32..b02e2af73c9ea7fbc66e0c212c1a5c7bc1819058 100644
--- a/runtime/vm/thread_interrupter_macos.cc
+++ b/runtime/vm/thread_interrupter_macos.cc
@@ -47,7 +47,8 @@ void ThreadInterrupter::InterruptThread(InterruptableThreadState* state) {
   if (FLAG_trace_thread_interrupter) {
     OS::Print("ThreadInterrupter interrupting %p\n", state->id);
   }
-  pthread_kill(state->id, SIGPROF);
+  int result = pthread_kill(state->id, SIGPROF);
+  ASSERT(result == 0);
 }