Add support for FastLRUCache in cache_bench (#10095)

Add support for FastLRUCache in cache_bench (#10095)

Summary:
cache_bench can now run with FastLRUCache.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10095

Test Plan:
- Temporarily add an ``assert(false)`` in the execution path that sets up the FastLRUCache. Run ``make -j24 cache_bench``. Then test the appropriate code is used by running ``./cache_bench -cache_type=fast_lru_cache`` and checking that the assert is called. Repeat for LRUCache.
- Verify that FastLRUCache (currently a clone of LRUCache) has similar latency distribution than LRUCache, by comparing the outputs of ``./cache_bench -cache_type=fast_lru_cache`` and ``./cache_bench -cache_type=lru_cache``.

Reviewed By: pdillinger

Differential Revision: D36875834

Pulled By: guidotag

fbshipit-source-id: eb2ad0bb32c2717a258a6ac66ed736e06f826cd8