Summary:
This diff is revamping our build tools:
1) Use third-party2 instead of third-party
2) consolidate clang and gcc scripts together, lots of duplication there
3) remove hdfs libs, we never compile rocksdb with them
clang compilation doesn't work yet. It doesn't work in master either. I plan to fix it soon, but I just spent 2 hours trying to make it work and failed. I'll ask experts.
Test Plan: compiles with gcc
Reviewers: ljin, yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D28047
