src/CMakeLists.txt:

src/CMakeLists.txt:

The Rocksdb code under Clang complains about:
/home/jenkins/workspace/ceph-master/src/rocksdb/util/thread_local.h:205:5:
  error: macro expansion producing 'defined' has undefined behavior
  [-Werror,-Wexpansion-to-defined]
    ^
/home/jenkins/workspace/ceph-master/src/rocksdb/util/thread_local.h:22:4:
  note: expanded from macro 'ROCKSDB_SUPPORT_THREAD_LOCAL'
  !defined(OS_WIN) && !defined(OS_MACOSX) && !defined(IOS_CROSS_COMPILE)
   ^`
So under Clang disable -Werror

Signed-off-by: Willem Jan Withagen <wjw@digiware.nl>