Summary: We need this because we build MySQL with 4.8.1.
Test Plan: ROCKSDB_FBCODE_BUILD_WITH_481=1 make check
Reviewers: sdong, yhchiang, rven, yoshinorim
Reviewed By: yoshinorim
Subscribers: jonahcohen, yoshinorim, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D32073
