Mute an UBSan check error for SCOPED_LOCK macro (#283)

thread/thread.cpp

@@ -72,8 +72,6 @@ inline int posix_memalign(void** memptr, size_t alignment, size_t size) {
  by target vcpu in resume_thread(), when its runq becomes empty;
 */
 
-#define SCOPED_MEMBER_LOCK(x) SCOPED_LOCK(&(x)->lock, ((bool)x) * 2)
-
 // Define assembly section header for clang and gcc
 #if defined(__APPLE__)
 #define DEF_ASM_FUNC(name) ".text\n" \
@@ -1199,7 +1197,8 @@ R"(
  __attribute__((always_inline)) inline
  Switch prepare_usleep(uint64_t useconds, thread_list* waitq, RunQ rq = {})
  {
- SCOPED_MEMBER_LOCK(waitq);
+ spinlock* waitq_lock = waitq ? &waitq->lock : nullptr;
+ SCOPED_LOCK(waitq_lock, ((bool) waitq) * 2);
  SCOPED_LOCK(rq.current->lock);
  assert(!AtomicRunQ(rq).single());
  auto sw = AtomicRunQ(rq).remove_current(states::SLEEPING);