HAWQ-1226. fix compile error under gcc 4.8.2
HAWQ-1226. fix compile error under gcc 4.8.2

huor/incubator-hawq,jianlirong/incubator-hawq,lavjain/incubator-hawq,wengyanqing/incubator-hawq,wengyanqing/incubator-hawq,huor/incubator-hawq,stanlyxiang/incubator-hawq,jianlirong/incubator-hawq,huor/incubator-hawq,huor/incubator-hawq,outofmem0ry/incubator-hawq,outofmem0ry/incubator-hawq,jianlirong/incubator-hawq,jianlirong/incubator-hawq,jianlirong/incubator-hawq,stanlyxiang/incubator-hawq,jianlirong/incubator-hawq,huor/incubator-hawq,lavjain/incubator-hawq,outofmem0ry/incubator-hawq,huor/incubator-hawq,wengyanqing/incubator-hawq,stanlyxiang/incubator-hawq,jianlirong/incubator-hawq,stanlyxiang/incubator-hawq,outofmem0ry/incubator-hawq,outofmem0ry/incubator-hawq,wengyanqing/incubator-hawq,stanlyxiang/incubator-hawq,lavjain/incubator-hawq,lavjain/incubator-hawq,outofmem0ry/incubator-hawq,huor/incubator-hawq,stanlyxiang/incubator-hawq,wengyanqing/incubator-hawq,lavjain/incubator-hawq,wengyanqing/incubator-hawq,lavjain/incubator-hawq,outofmem0ry/incubator-hawq,lavjain/incubator-hawq,outofmem0ry/incubator-hawq,wengyanqing/incubator-hawq,lavjain/incubator-hawq,jianlirong/incubator-hawq,wengyanqing/incubator-hawq,stanlyxiang/incubator-hawq