I ended up installing RXTX from the Angrstrom distribution by adding the following to /etc/opkg/angstrom-feed.conf:
src/gz base http://www.angstrom-distribution.org/feeds/2011.03/ipk/glibc/armv5te/base
I then used opkg to install the program.
Not my preferred way of doing it, but it works for now until I can find time to research the compile issue further.
Regards,
Rob