Test Plan:
Built and ran with gflags:
% ./db_bench
LevelDB: version 4.5
Date: Tue Feb 16 12:04:23 2016
CPU: 40 * Intel(R) Xeon(R) CPU E5-2660 v2 @ 2.20GHz
...
And without gflags:
% ./db_bench
Please install gflags to run rocksdb tools
%
Reviewers: sdong, igor
Reviewed By: igor
Subscribers: igor, dhruba
Differential Revision: https://reviews.facebook.net/D54243