Make rocksdb work with all versions of lz4

Summary:
There are some projects in fbcode that define lz4 dependency on r108. We, however, defined dependency on r117. That produced some interesting issues and our build system was not happy.

This diff makes rocksdb work with both r108 and r117. Hopefully this will fix our problems.

Test Plan: compiled rocksdb with both r108 and r117 lz4

Reviewers: dhruba, sdong, haobo

Reviewed By: sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18465