For the record, XEmacs builds just fine (for me :) on Solaris 2.5.1
and Solaris 2.6, with similar configurations (gcc 2.8, CFLAGS=-O3. mule)
If you're mixing Solaris' OpenWindows with a grafted-on X11R6, you can
expect surprises. Someone who runs such a configuration will have to
debug it. I've always figured that the whole point to running Solaris
was to get the (by now) reasonably stable, industry standard OS, and
not muck around too much with system components like X11.
If you are the adventurous type, and native Solaris is too dull, why
not choose Linux/Sparc? Or at least Solaris 2.6, which comes with
X11R6, and a raft of cool new bugs?
Martin