Fix compilation error with gcc 4.7
Fix compilation error with gcc 4.7

Summary:
Fix compilation error with gcc 4.7

Test Plan:
make clean
make

Reviewers:

CC:

Task ID: #

Blame Rev:

OverlordQ/rocksdb,virtdb/rocksdb,temicai/rocksdb,amyvmiwei/rocksdb,norton/rocksdb,NickCis/rocksdb,wenduo/rocksdb,OverlordQ/rocksdb,luckywhu/rocksdb,sorphi/rocksdb,vashstorm/rocksdb,JackLian/rocksdb,virtdb/rocksdb,hobinyoon/rocksdb,fengshao0907/rocksdb,amyvmiwei/rocksdb,alihalabyah/rocksdb,NickCis/rocksdb,rDSN-Projects/rocksdb.replicated,zhangpng/rocksdb,tsheasha/rocksdb,mbarbon/rocksdb,vmx/rocksdb,IMCG/RcoksDB,vmx/rocksdb,anagav/rocksdb,virtdb/rocksdb,NickCis/rocksdb,sorphi/rocksdb,ylong/rocksdb,rDSN-Projects/rocksdb.replicated,jalexanderqed/rocksdb,ylong/rocksdb,norton/rocksdb,mbarbon/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,skunkwerks/rocksdb,ylong/rocksdb,flabby/rocksdb,Vaisman/rocksdb,kaschaeffer/rocksdb,wskplho/rocksdb,msb-at-yahoo/rocksdb,zhangpng/rocksdb,IMCG/RcoksDB,wenduo/rocksdb,IMCG/RcoksDB,NickCis/rocksdb,biddyweb/rocksdb,alihalabyah/rocksdb,wat-ze-hex/rocksdb,mbarbon/rocksdb,makelivedotnet/rocksdb,anagav/rocksdb,temicai/rocksdb,JackLian/rocksdb,ryneli/rocksdb,wenduo/rocksdb,wlqGit/rocksdb,amyvmiwei/rocksdb,luckywhu/rocksdb,bbiao/rocksdb,dkorolev/rocksdb,JackLian/rocksdb,zhangpng/rocksdb,lgscofield/rocksdb,mbarbon/rocksdb,ylong/rocksdb,biddyweb/rocksdb,amyvmiwei/rocksdb,wat-ze-hex/rocksdb,JohnPJenkins/rocksdb,facebook/rocksdb,tizzybec/rocksdb,vmx/rocksdb,alihalabyah/rocksdb,makelivedotnet/rocksdb,siddhartharay007/rocksdb,biddyweb/rocksdb,tizzybec/rocksdb,JoeWoo/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,sorphi/rocksdb,vashstorm/rocksdb,caijieming-baidu/rocksdb,alihalabyah/rocksdb,luckywhu/rocksdb,IMCG/RcoksDB,Applied-Duality/rocksdb,ylong/rocksdb,msb-at-yahoo/rocksdb,wenduo/rocksdb,geraldoandradee/rocksdb,vashstorm/rocksdb,wat-ze-hex/rocksdb,tsheasha/rocksdb,anagav/rocksdb,JohnPJenkins/rocksdb,skunkwerks/rocksdb,JoeWoo/rocksdb,wenduo/rocksdb,ryneli/rocksdb,tsheasha/rocksdb,kaschaeffer/rocksdb,caijieming-baidu/rocksdb,tsheasha/rocksdb,rDSN-Projects/rocksdb.replicated,luckywhu/rocksdb,JoeWoo/rocksdb,wat-ze-hex/rocksdb,caijieming-baidu/rocksdb,SunguckLee/RocksDB,kaschaeffer/rocksdb,amyvmiwei/rocksdb,JackLian/rocksdb,wlqGit/rocksdb,tizzybec/rocksdb,tizzybec/rocksdb,fengshao0907/rocksdb,skunkwerks/rocksdb,RyanTech/rocksdb,tschottdorf/rocksdb,geraldoandradee/rocksdb,wskplho/rocksdb,NickCis/rocksdb,hobinyoon/rocksdb,makelivedotnet/rocksdb,geraldoandradee/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,dkorolev/rocksdb,wskplho/rocksdb,makelivedotnet/rocksdb,wlqGit/rocksdb,wat-ze-hex/rocksdb,temicai/rocksdb,SunguckLee/RocksDB,skunkwerks/rocksdb,wat-ze-hex/rocksdb,norton/rocksdb,Andymic/rocksdb,facebook/rocksdb,fengshao0907/rocksdb,wlqGit/rocksdb,wlqGit/rocksdb,OverlordQ/rocksdb,zhangpng/rocksdb,ryneli/rocksdb,mbarbon/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,fengshao0907/rocksdb,siddhartharay007/rocksdb,ryneli/rocksdb,jalexanderqed/rocksdb,zhangpng/rocksdb,norton/rocksdb,siddhartharay007/rocksdb,caijieming-baidu/rocksdb,IMCG/RcoksDB,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,alihalabyah/rocksdb,temicai/rocksdb,flabby/rocksdb,zhangpng/rocksdb,NickCis/rocksdb,makelivedotnet/rocksdb,Andymic/rocksdb,wskplho/rocksdb,luckywhu/rocksdb,NickCis/rocksdb,vmx/rocksdb,bbiao/rocksdb,sorphi/rocksdb,Applied-Duality/rocksdb,Andymic/rocksdb,siddhartharay007/rocksdb,norton/rocksdb,RyanTech/rocksdb,bbiao/rocksdb,flabby/rocksdb,Andymic/rocksdb,bbiao/rocksdb,anagav/rocksdb,jalexanderqed/rocksdb,ylong/rocksdb,norton/rocksdb,tsheasha/rocksdb,ryneli/rocksdb,lgscofield/rocksdb,IMCG/RcoksDB,virtdb/rocksdb,skunkwerks/rocksdb,rDSN-Projects/rocksdb.replicated,bbiao/rocksdb,tschottdorf/rocksdb,facebook/rocksdb,luckywhu/rocksdb,mbarbon/rocksdb,dkorolev/rocksdb,tsheasha/rocksdb,mbarbon/rocksdb,kaschaeffer/rocksdb,wat-ze-hex/rocksdb,Applied-Duality/rocksdb,RyanTech/rocksdb,virtdb/rocksdb,vashstorm/rocksdb,geraldoandradee/rocksdb,tschottdorf/rocksdb,msb-at-yahoo/rocksdb,vmx/rocksdb,jalexanderqed/rocksdb,Vaisman/rocksdb,kaschaeffer/rocksdb,lgscofield/rocksdb,dkorolev/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,norton/rocksdb,skunkwerks/rocksdb,lgscofield/rocksdb,ylong/rocksdb,RyanTech/rocksdb,rDSN-Projects/rocksdb.replicated,tschottdorf/rocksdb,tsheasha/rocksdb,JackLian/rocksdb,dkorolev/rocksdb,biddyweb/rocksdb,fengshao0907/rocksdb,JackLian/rocksdb,hobinyoon/rocksdb,anagav/rocksdb,rDSN-Projects/rocksdb.replicated,jalexanderqed/rocksdb,kaschaeffer/rocksdb,lgscofield/rocksdb,JohnPJenkins/rocksdb,ryneli/rocksdb,makelivedotnet/rocksdb,IMCG/RcoksDB,sorphi/rocksdb,flabby/rocksdb,bbiao/rocksdb,wlqGit/rocksdb,Andymic/rocksdb,amyvmiwei/rocksdb,wskplho/rocksdb,facebook/rocksdb,norton/rocksdb,caijieming-baidu/rocksdb,skunkwerks/rocksdb,temicai/rocksdb,JoeWoo/rocksdb,alihalabyah/rocksdb,Vaisman/rocksdb,Andymic/rocksdb,OverlordQ/rocksdb,sorphi/rocksdb,Vaisman/rocksdb,tizzybec/rocksdb,RyanTech/rocksdb,Applied-Duality/rocksdb,Applied-Duality/rocksdb,makelivedotnet/rocksdb,JohnPJenkins/rocksdb,alihalabyah/rocksdb,vmx/rocksdb,JackLian/rocksdb,wskplho/rocksdb,tizzybec/rocksdb,tschottdorf/rocksdb,geraldoandradee/rocksdb,geraldoandradee/rocksdb,geraldoandradee/rocksdb,wenduo/rocksdb,msb-at-yahoo/rocksdb,wlqGit/rocksdb,caijieming-baidu/rocksdb,Andymic/rocksdb,facebook/rocksdb,siddhartharay007/rocksdb,OverlordQ/rocksdb,amyvmiwei/rocksdb,vashstorm/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,rDSN-Projects/rocksdb.replicated,RyanTech/rocksdb,flabby/rocksdb,facebook/rocksdb,sorphi/rocksdb,anagav/rocksdb,dkorolev/rocksdb,flabby/rocksdb,anagav/rocksdb,RyanTech/rocksdb,wskplho/rocksdb,temicai/rocksdb,lgscofield/rocksdb,vashstorm/rocksdb,msb-at-yahoo/rocksdb,luckywhu/rocksdb,biddyweb/rocksdb,Applied-Duality/rocksdb,tsheasha/rocksdb,fengshao0907/rocksdb,tizzybec/rocksdb,JohnPJenkins/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,wenduo/rocksdb,msb-at-yahoo/rocksdb,JoeWoo/rocksdb,flabby/rocksdb,Applied-Duality/rocksdb,siddhartharay007/rocksdb,jalexanderqed/rocksdb,zhangpng/rocksdb,virtdb/rocksdb,siddhartharay007/rocksdb,facebook/rocksdb,tschottdorf/rocksdb,dkorolev/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,vashstorm/rocksdb,Vaisman/rocksdb,caijieming-baidu/rocksdb,Vaisman/rocksdb,bbiao/rocksdb,hobinyoon/rocksdb,JohnPJenkins/rocksdb,fengshao0907/rocksdb,Vaisman/rocksdb,kaschaeffer/rocksdb,facebook/rocksdb,lgscofield/rocksdb,wat-ze-hex/rocksdb,biddyweb/rocksdb,biddyweb/rocksdb,JoeWoo/rocksdb,virtdb/rocksdb,JoeWoo/rocksdb,temicai/rocksdb,JohnPJenkins/rocksdb