Initialize variable in constructor for PosixEnv::checkedDiskForMmap_
Initialize variable in constructor for PosixEnv::checkedDiskForMmap_

Summary: This caused compilation problems on some gcc platforms during the third-partyrelease

Test Plan: make

Reviewers: sheki

Reviewed By: sheki

Differential Revision: https://reviews.facebook.net/D9627

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