Summary:
RocksDB is compiled as part of MyRocks (MySQL storage engine) build.
MySQL already defines `CACHE_LINE_SIZE` and therefore we're getting a
conflict. Change RocksDB definition to be more cognizant of this.
Closes https://github.com/facebook/rocksdb/pull/2257
Differential Revision: D5013188
Pulled By: gunnarku
fbshipit-source-id: cfa76fe99f90dcd82aa09204e2f1f35e07a82b41