Summary:
Pinned the alignment of StatisticsData to the cacheline size rather than just extending its size (which could go over two cache lines)if unaligned in allocation.

Avoid compile errors in the process as per individual commit messages.

strengthen static_assert to CACHELINE rather than the highest common multiple.
Closes https://github.com/facebook/rocksdb/pull/4036

Differential Revision: D8582844

Pulled By: yiwu-arbug

fbshipit-source-id: 363c37029f28e6093e06c60b987bca9aa204bc71