Sorry; I don't have the time to fix this. Might be a trivial fix... don't know. On the download page there did not appear to be a list of required packages; If 'hdl' is due to a missing package dependency then please list it on the download page.

$ make [...] ao_sndio.c: In function ao_plugin_open': ao_sndio.c:103: error: hdl' undeclared (first use in this function)

$ uname -srvm OpenBSD 4.5 GENERIC#1749 i386

$ find /usr/include -exec grep -q -e hdl ;-print -exec grep -n -e hdl ; /usr/include/dev/audio_if.h 136: void *hdl; [... not relevant ...]

nothing in /usr/local/include and /include is non-existant