tsan: prevent insertion of memset into BenignRaceImpl

[dvyukov]

Summary

Some bots started failing with the following error
after changing Alloc to New. Change it back.

ThreadSanitizer: CHECK failed: ((locked[i].recursion)) == ((0))
4 sanitizer::CheckedMutex::CheckNoLocks()
5 tsan::ScopedInterceptor::~ScopedInterceptor()
6 memset
7 tsan::New<tsan::ExpectRace>()
8 __tsan::AddExpectRace()
9 BenignRaceImpl()

compiler-rt/lib/tsan/rtl/tsan_interface_ann.cpp

static void AddExpectRace(ExpectRace *list,
   ExpectRace *race = list->next;
   for (; race != list; race = race->next) {
     if (race->addr == addr && race->size == size) {
       atomic_store_relaxed(&race->addcount,
           atomic_load_relaxed(&race->addcount) + 1);
       return;
     }
   }
-  race = New<ExpectRace>();
+  race = static_cast<ExpectRace *>(Alloc(sizeof(ExpectRace)));
   race->addr = addr;
   race->size = size;
   race->file = f;
   race->line = l;
   race->desc[0] = 0;
   atomic_store_relaxed(&race->hitcount, 0);
   atomic_store_relaxed(&race->addcount, 1);
   if (desc) {