Fix compile error on platform010

[guowentian]

We have recently switched to using platform010 #11333. Now the main branch has compilation error mainly because std::reference_wrapper is not compatible when we are expecting the type T.

Examples of errors:

cache/cache_bench_tool.cc:618:12: error: format ‘%u’ expects argument of type ‘unsigned int’, but argument 2 has type ‘std::reference_wrapper<unsigned int>’ [-Werror=format=]
     printf("Number of threads   : %u\n", FLAGS_threads);

cache/cache_bench_tool.cc:722:28: error: use of deleted function ‘std::reference_wrapper<_Tp>::reference_wrapper(_Tp&&) [with _Tp = unsigned int]’
       FLAGS_sck_db_count = 1;

cache/cache_bench_tool.cc:773:16: error: format ‘%u’ expects argument of type ‘unsigned int’, but argument 4 has type ‘std::reference_wrapper<unsigned int>’ [-Werror=format=]
         printf("%" PRIu64
                ^~~~~~~~~~
                " collisions after %d x %u days, est %g days between (%g "
                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                "corrected)        \n",
                ~~~~~~~~~~~~~~~~~~~~~~
                collisions_, i, FLAGS_sck_days_per_run, est, est * multiplier_);

Hereby, fix the error by using .get() method

[guowentian]

The compilation can pass locally, but fail in circleci. Not sure why. It seems clang++ can't recognize .get() member function