Fix compiler warning in frontend.h
Fix compiler warning in frontend.h

henryr/Impala,lirui-intel/Impala,lirui-intel/Impala,bowlofstew/Impala,cchanning/Impala,lnliuxing/Impala,ImpalaToGo/ImpalaToGo,cloudera/recordservice,gerashegalov/Impala,andybab/Impala,cgvarela/Impala,ibmsoe/ImpalaPPC,ImpalaToGo/ImpalaToGo,bratatidas9/Impala-1,andybab/Impala,theyaa/Impala,ibmsoe/ImpalaPPC,XiaominZhang/Impala,kapilrastogi/Impala,XiaominZhang/Impala,gerashegalov/Impala,cloudera/recordservice,gerashegalov/Impala,grundprinzip/Impala,mapr/impala,caseyching/Impala,AtScaleInc/Impala,tempbottle/Impala,lnliuxing/Impala,theyaa/Impala,rdblue/Impala,caseyching/Impala,cgvarela/Impala,mapr/impala,tempbottle/Impala,placrosse/ImpalaToGo,grundprinzip/Impala,bowlofstew/Impala,gistic/PublicSpatialImpala,XiaominZhang/Impala,placrosse/ImpalaToGo,tempbottle/Impala,lirui-intel/Impala,gistic/PublicSpatialImpala,rdblue/Impala,bowlofstew/Impala,bratatidas9/Impala-1,grundprinzip/Impala,lnliuxing/Impala,henryr/Impala,caseyching/Impala,gerashegalov/Impala,bratatidas9/Impala-1,rampage644/impala-cut,caseyching/Impala,andybab/Impala,rdblue/Impala,cchanning/Impala,bowlofstew/Impala,theyaa/Impala,rampage644/impala-cut,brightchen/Impala,XiaominZhang/Impala,scalingdata/Impala,kapilrastogi/Impala,tempbottle/Impala,lirui-intel/Impala,bowlofstew/Impala,caseyching/Impala,bratatidas9/Impala-1,placrosse/ImpalaToGo,grundprinzip/Impala,gerashegalov/Impala,cchanning/Impala,grundprinzip/Impala,gerashegalov/Impala,caseyching/Impala,bowlofstew/Impala,AtScaleInc/Impala,rdblue/Impala,gistic/PublicSpatialImpala,bratatidas9/Impala-1,cloudera/recordservice,XiaominZhang/Impala,AtScaleInc/Impala,scalingdata/Impala,cloudera/recordservice,brightchen/Impala,andybab/Impala,XiaominZhang/Impala,theyaa/Impala,scalingdata/Impala,cloudera/recordservice,scalingdata/Impala,rdblue/Impala,bowlofstew/Impala,cgvarela/Impala,theyaa/Impala,kapilrastogi/Impala,bratatidas9/Impala-1,lnliuxing/Impala,cgvarela/Impala,caseyching/Impala,lnliuxing/Impala,rdblue/Impala,lirui-intel/Impala,lirui-intel/Impala,theyaa/Impala,ibmsoe/ImpalaPPC,brightchen/Impala,brightchen/Impala,henryr/Impala,cchanning/Impala,mapr/impala,rampage644/impala-cut,lnliuxing/Impala,placrosse/ImpalaToGo,cgvarela/Impala,lnliuxing/Impala,brightchen/Impala,tempbottle/Impala,ImpalaToGo/ImpalaToGo,AtScaleInc/Impala,XiaominZhang/Impala,ibmsoe/ImpalaPPC,tempbottle/Impala,scalingdata/Impala,gistic/PublicSpatialImpala,kapilrastogi/Impala,tempbottle/Impala,scalingdata/Impala,cgvarela/Impala,grundprinzip/Impala,gistic/PublicSpatialImpala,AtScaleInc/Impala,lirui-intel/Impala,cloudera/recordservice,cchanning/Impala,kapilrastogi/Impala,cchanning/Impala,rdblue/Impala,gistic/PublicSpatialImpala,andybab/Impala,henryr/Impala,rampage644/impala-cut,placrosse/ImpalaToGo,ibmsoe/ImpalaPPC,mapr/impala,brightchen/Impala,andybab/Impala,placrosse/ImpalaToGo,cgvarela/Impala,gerashegalov/Impala,henryr/Impala,kapilrastogi/Impala,rampage644/impala-cut,bratatidas9/Impala-1,cloudera/recordservice,ibmsoe/ImpalaPPC,AtScaleInc/Impala,brightchen/Impala,kapilrastogi/Impala,henryr/Impala,mapr/impala,ibmsoe/ImpalaPPC,theyaa/Impala,cchanning/Impala,rampage644/impala-cut,ImpalaToGo/ImpalaToGo,ImpalaToGo/ImpalaToGo,ImpalaToGo/ImpalaToGo