message: fix windows kokoro build
diff: @@ -110,8 +110,8 @@ const char *getActivityUnifiedMemoryKindString(
  // GetCachedTID() caches the thread ID in thread-local storage (which is a
  // userspace construct) to avoid unnecessary system calls. Without this caching,
  // it can take roughly 98ns, while it takes roughly 1ns with this caching.
  -pid_t GetCachedTID() {
  - static thread_local pid_t current_thread_id =
  +int32 GetCachedTID() {
  + static thread_local int32 current_thread_id =
  Env::Default()->GetCurrentThreadId();
  return current_thread_id;
  }
  