Oops!  

Looking at your make output, Zack, and comparing with my copy of the
source, it starts to become evident that various key definitions are
not being seen.

Upon further investigation, I uncovered the suggestion that I must
have made another few small changes in the nas-1.2p5 source tree
before I got a usable build out of it.

Firstly, as has already been reported, there's the fix to
./lib/audio/Alibint.c to use the __NetBSD__ macro as a conditional
compilation guard.  The only other suggestions that I can offer do
likewise in different files.  The second file to poke about in is
./server/dda/voxware/auvoxware.c, around line 170.  I can't offer a
patch because I don't seem to have kept a copy of the original, but
you should see something like:

#ifdef __FreeBSD__
#include <machine/soundcard.h>
#include <machine/pcaudioio.h>
#else
# include <sys/soundcard.h>
#endif

which I made to look like this:

#ifdef __FreeBSD__
#include <machine/soundcard.h>
#include <machine/pcaudioio.h>
#else
# ifdef __NetBSD__
#  include <soundcard.h>
#  include <sys/ioctl.h>
# else
#  include <sys/soundcard.h>
# endif
#endif



Lastly, there's ./server/dia/au.h, line 36.  Once again, I didn't keep 
an original, so I can give you no patch, but, change line 36 from
something like:

#if defined(__FreeBSD__) || defined(linux) || (defined(SVR4) && defined(SYSV386))

into something like:

#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(linux) || (defined(SVR4) && defined(SYSV386))

This is more than likely suboptimal WRT platform independence, but the
implication is that this is an i386 port.  Perhaps that fact should be
reflected as a part the guard condition.

Good luck this time!

--Kevin.