The Slackware64 multilib installation includes the required GTK+ 2 (>=2.4). However, attempting to run LispWorks gives the following error message:
$ /usr/local/lib/LispWorks/lispworks-6-1-0-x86-linux (lispworks:30162): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory This likely means that your installation is broken. Try running the command gdk-pixbuf-query-loaders \ > /usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache to make things work again for the time being. ...
To remedy this, I ran the 32-bit_version of gdk-pixbuf-query-loaders(1):
$ su - # gdk-pixbuf-query-loaders-32 \ > /usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache
Following that, LispWorks started without incident.