In QEMU 4 or higher you can no longer use the normal "-soundhw ac97" flag and it is much more complicated but here is a simple copy and paste on Linux that will just work:
-audiodev you have to use -audiodev to specify the driver and id
driver=pa
id=someid
-device you have to specify the same audiodev id you used in -audiodev and driver
-audiodev driver=pa,id=pa1 -devic........