For #1250, support osx build
For #1250, support osx build

ossrs/srs,winlinvip/srs,winlinvip/srs,ossrs/srs,winlinvip/srs,winlinvip/srs,ossrs/srs,ossrs/srs,winlinvip/srs,winlinvip/simple-rtmp-server,ossrs/srs,winlinvip/srs,ossrs/srs