C++11 requires <atomic>. This lets us remove the header detection (LEVELDB_ATOMIC_PRESENT) and simplify port/atomic_pointer.h. ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=189919098
Fixes https://github.com/google/leveldb/issues/466 ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=189425354