Fix release build caused by #7067 (#7077)

Summary:
The issue is introduced by https://github.com/facebook/rocksdb/issues/7067

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7077

Test Plan: `make release`

Reviewed By: pdillinger

Differential Revision: D22370835

Pulled By: jay-zhuang

fbshipit-source-id: 44326bae07809c4518371b6a7d1f47124e24a4f3

db_stress_tool/db_stress_test_base.cc

@@ -14,6 +14,7 @@
 #include "db_stress_tool/db_stress_driver.h"
 #include "rocksdb/convenience.h"
 #include "rocksdb/sst_file_manager.h"
+#include "util/cast_util.h"
 
 namespace ROCKSDB_NAMESPACE {
 StressTest::StressTest()