fixed VFG's support for interfunction_level
fixed VFG's support for interfunction_level

iamahuman/angr,axt/angr,iamahuman/angr,angr/angr,f-prettyland/angr,chubbymaggie/angr,fjferrer/angr,schieb/angr,chubbymaggie/angr,cureHsu/angr,xurantju/angr,avain/angr,GuardianRG/angr,f-prettyland/angr,angr/angr,tyb0807/angr,fjferrer/angr,GuardianRG/angr,angr/angr,haylesr/angr,tyb0807/angr,chubbymaggie/angr,haylesr/angr,xurantju/angr,iamahuman/angr,terry2012/angr,avain/angr,zhuyue1314/angr,terry2012/angr,mingderwang/angr,mingderwang/angr,zhuyue1314/angr,schieb/angr,schieb/angr,lowks/angr,lowks/angr,axt/angr,cureHsu/angr,f-prettyland/angr,tyb0807/angr,axt/angr