fix bug for build under centos5.5
fix bug for build under centos5.5

ossrs/srs-bench,simple-rtmp-server/srs-bench,winlinvip/srs-bench,myself659/st-load,winlinvip/srs-bench,simple-rtmp-server/srs-bench,myself659/st-load,winlinvip/st-load,winlinvip/st-load,ossrs/srs-bench,ossrs/srs-bench