Summary:
This PR adds support for building on s390x including updating travis CI. It uses the previous work in https://github.com/facebook/rocksdb/pull/6168 and adds some more changes to get all current tests (make check and jni tests) to pass. The tests were run with snappy, lz4, bzip2 and zstd all compiled in.

There are a few pieces still needed to get the travis build working that I don't think I can do. adamretter is this something you could help with?

1. A prebuilt https://rocksdb-deps.s3-us-west-2.amazonaws.com/cmake/cmake-3.14.5-Linux-s390x.deb package
2. A https://hub.docker.com/r/evolvedbinary/rocksjava s390x image

Not sure if there is more required for travis. Happy to help in any way I can.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8962

Reviewed By: mrambacher

Differential Revision: D31802198

Pulled By: pdillinger

fbshipit-source-id: 683511466fa6b505f85ba5a9964a268c6151f0c2