[jpstewart]

Interesting.  I've been poking around in the GL libraries on my Octane.  It seems libGLcore.so does have an undefined symbol gl_INTERPRET_END.  But I can't find which library it is defined in.  It must be defined somewhere!

The undefined XSGI symbols are in libXext.so.  That needs to be included in the list of libraries when you're seeing those errors.

Since partitionpenguin is using GNU ld order should not matter, but for IRIX ld libXext must be after the GL libraries.

I'm thinking that glCore is not meant to ever be used directly in linker flags

Correct.  What does 'ldd /usr/lib32/libGL.so' output?  It should list libGLcore.so as one of the libraries used by libGL -- which is exactly why you shouldn't need to add it to the linker command.  Maybe also try using IRIX ld instead, if you can.  This might be a bug in the GNU linker.