Summary:
clang compilation is failing due to a4fb1f8c04. In that commit I added a call to `std::atomic::is_lock_free` which was evidently relying on a compiler builtin only present in gcc.
Drawbacks to this fix are:
- users may need to install libatomic
- there might be cases where clang is used even though USE_CLANG is unset (e.g., when clang is the only available compiler). I didn't figure out how to add -latomic in those cases...
An alternative fix mentioned in http://lists.llvm.org/pipermail/llvm-bugs/2017-August/057263.html is using -stdlib=libc++ with clang.
Closes https://github.com/facebook/rocksdb/pull/3769
Differential Revision: D7756261
Pulled By: ajkr
fbshipit-source-id: 26888300683fa9970ab5950239d1aa217e8efd49
9b89479e64