message: Make Transactions_Threaded* run faster on Mac
diff: @@ -352,7 +352,7 @@ TEST(Transactions_Threaded)
  tk = table->get_key();
  wt->commit();
  }
  -#if defined(_WIN32) || REALM_ANDROID
  +#if defined(_WIN32) || REALM_ANDROID || REALM_PLATFORM_APPLE
  const int num_threads = 2;
  #else
  const int num_threads = 20;
  @@ -385,7 +385,7 @@ TEST(Transactions_ThreadedAdvanceRead)
  tk = table->get_key();
  wt->commit();
  }
  -#if defined(_WIN32) || REALM_ANDROID
  +#if defined(_WIN32) || REALM_ANDROID || REALM_PLATFORM_APPLE
  const int num_threads = 2;
  #else
  const int num_threads = 20;
  