Autoconf is limping on Rhapsody5.3, we need to take glib/gtk+ out and get libIDL building. See the Unix Build page for more info.
The default compiler shipped with Rhapsody 1.0 is gcc-2.7.2.1, Solaris gcc-2.7.2.3 works so we're not that far off the mark. A current version of egcs would be a much stronger compiler.
What needs to happen next?
Fill in holes in NGLayout backend.
Follow the lead of one of the other toolkits to get started here.