Ran into fewer errors this time, but still no go. Here's what it threw at me:
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I/usr/local/include/glib12 -c testasync.c
In file included from asyncdns.h:9,
from testasync.c:8:
/usr/include/arpa/inet.h:89: warning: parameter has incomplete type
/usr/include/arpa/inet.h:92: warning: parameter has incomplete type
/usr/include/arpa/inet.h:96: warning: parameter has incomplete type
testasync.c: In function `dns_callback':
testasync.c:37: invalid use of undefined type `struct in_addr'
testasync.c:37: type of formal parameter 1 is incomplete
gmake[2]: *** [testasync.o] Error 1

I hope I'm being helpful.