VM: Small clean up and const-ness fix for Thread/OSThread constants.

runtime/bin/thread_win.cc

Index: runtime/bin/thread_win.cc
diff --git a/runtime/bin/thread_win.cc b/runtime/bin/thread_win.cc
index 05949a1eab0e0c3859504d12c464005f2909cfff..44941bbf22fa6c007709a5f46d45a462ffd3f726 100644
--- a/runtime/bin/thread_win.cc
+++ b/runtime/bin/thread_win.cc
@@ -70,8 +70,8 @@ int Thread::Start(ThreadStartFunction function, uword parameter) {
   return 0;
 }
 
-ThreadLocalKey Thread::kUnsetThreadLocalKey = TLS_OUT_OF_INDEXES;
-ThreadId Thread::kInvalidThreadId = 0;
+const ThreadLocalKey Thread::kUnsetThreadLocalKey = TLS_OUT_OF_INDEXES;
+const ThreadId Thread::kInvalidThreadId = 0;
 
 ThreadLocalKey Thread::CreateThreadLocal() {
   ThreadLocalKey key = TlsAlloc();