For what it's worth, I got around this by deleting the GTK package.
The problem seems to have been due to my rebuild of my system on
Tuesday having somehow made the installed GTK package unsuitable for
use by xmms.  

James Wetterau says:
...> 
> ------- Forwarded Message
> ...
> > James Wetterau <jwjr@panix.com> writes:
> > 
> > > I'm receiving the following error when trying to build xmms from
> > > pkgsrc, running -current (rebuilt today).
> > > 
> > > checking for GTK - version >= 1.2.2... no
> > > *** Could not run GTK test program, checking why...
> > > *** The test program compiled, but did not run. This usually means
> > > *** that the run-time linker is not finding GTK or finding the wrong
> > > *** version of GTK. If it is not finding GTK, you'll need to set your
> > > *** LD_LIBRARY_PATH environment variable, or edit /etc/ld.so.conf to
...
> ------- End of Forwarded Message