Support older versions of libao.
Support older versions of libao.

albertz/shairport,albertz/shairport,mspasov/shairport,bowlofstew/shairport,IronBeard/shairport,skaman/shairport,IronBeard/shairport,IronBeard/shairport,bowlofstew/shairport,bowlofstew/shairport,narakai/shairport,dotmpe/shairport,dotmpe/shairport,mspasov/shairport,narakai/shairport,hendrikw82/shairport,narakai/shairport,skaman/shairport,hendrikw82/shairport,hendrikw82/shairport,dotmpe/shairport