memprof: don't use thread user_id

[dvyukov]

Summary

memprof does not use user_id for anything,
so don't pass it to ThreadCreate.
Passing a random field of MemprofThread as user_id
does not make much sense anyway.

Depends on D113920.

compiler-rt/lib/memprof/memprof_thread.cpp

MemprofThread *MemprofThread::Create(thread_callback_t start_routine, void *arg,
                                      u32 parent_tid, StackTrace *stack,
                                      bool detached) {
   uptr PageSize = GetPageSizeCached();
   uptr size = RoundUpTo(sizeof(MemprofThread), PageSize);
   MemprofThread *thread = (MemprofThread *)MmapOrDie(size, __func__);
   thread->start_routine_ = start_routine;
   thread->arg_ = arg;
   MemprofThreadContext::CreateThreadContextArgs args = {thread, stack};
-  memprofThreadRegistry().CreateThread(*reinterpret_cast<uptr *>(thread),
-                                       detached, parent_tid, &args);
+  memprofThreadRegistry().CreateThread(0, detached, parent_tid, &args);
 
   return thread;
 }
 
 void MemprofThread::TSDDtor(void *tsd) {
   MemprofThreadContext *context = (MemprofThreadContext *)tsd;
   VReport(1, "T%d TSDDtor\n", context->tid);
   if (context->thread)