Convert nested_externs_aottest to use Halide::Buffer
Convert nested_externs_aottest to use Halide::Buffer

kgnk/Halide,ronen/Halide,ronen/Halide,kgnk/Halide,kgnk/Halide,ronen/Halide,ronen/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,ronen/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,ronen/Halide,ronen/Halide,ronen/Halide