Fix clang build
Fix clang build

Summary:
Missed this in https://reviews.facebook.net/D51633 because I didn't
wait for 'make commit-prereq' to finish

Test Plan: make clean && USE_CLANG=1 make -j32 all

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D52275

facebook/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,OverlordQ/rocksdb,tsheasha/rocksdb,flabby/rocksdb,tsheasha/rocksdb,vmx/rocksdb,facebook/rocksdb,norton/rocksdb,facebook/rocksdb,wenduo/rocksdb,Andymic/rocksdb,hobinyoon/rocksdb,hobinyoon/rocksdb,wenduo/rocksdb,Andymic/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,jalexanderqed/rocksdb,norton/rocksdb,wenduo/rocksdb,tsheasha/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,ryneli/rocksdb,wat-ze-hex/rocksdb,ryneli/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,Vaisman/rocksdb,Andymic/rocksdb,bbiao/rocksdb,bbiao/rocksdb,wenduo/rocksdb,wat-ze-hex/rocksdb,tsheasha/rocksdb,jalexanderqed/rocksdb,facebook/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,vmx/rocksdb,bbiao/rocksdb,flabby/rocksdb,Andymic/rocksdb,vmx/rocksdb,jalexanderqed/rocksdb,vmx/rocksdb,Vaisman/rocksdb,tsheasha/rocksdb,SunguckLee/RocksDB,hobinyoon/rocksdb,bbiao/rocksdb,ryneli/rocksdb,flabby/rocksdb,flabby/rocksdb,wenduo/rocksdb,bbiao/rocksdb,ryneli/rocksdb,tsheasha/rocksdb,norton/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,wenduo/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,norton/rocksdb,flabby/rocksdb,facebook/rocksdb,SunguckLee/RocksDB,ryneli/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,OverlordQ/rocksdb,norton/rocksdb,OverlordQ/rocksdb,jalexanderqed/rocksdb,ryneli/rocksdb,facebook/rocksdb,facebook/rocksdb,OverlordQ/rocksdb,OverlordQ/rocksdb,jalexanderqed/rocksdb,hobinyoon/rocksdb,norton/rocksdb,vmx/rocksdb,flabby/rocksdb,hobinyoon/rocksdb,hobinyoon/rocksdb,wat-ze-hex/rocksdb,ryneli/rocksdb,tsheasha/rocksdb,tsheasha/rocksdb,wat-ze-hex/rocksdb,norton/rocksdb,Vaisman/rocksdb,Andymic/rocksdb,bbiao/rocksdb,hobinyoon/rocksdb,wenduo/rocksdb,jalexanderqed/rocksdb,Vaisman/rocksdb,norton/rocksdb,Vaisman/rocksdb,flabby/rocksdb,Vaisman/rocksdb,SunguckLee/RocksDB,facebook/rocksdb,vmx/rocksdb,bbiao/rocksdb,Vaisman/rocksdb