BTW, I have almost been successful in getting GCC to work; it still relies on several header files (mainly those in sys/*) from the base Xenix system, which, of course, are only in the development system and won't work out of the box ('make install' chokes on the binary + source tarball of gcc-2.5.8 you can find online as it relies on system header files which are not there), you also need crt.o and sseg.o which can only be found in a really old binary of gcc-1.40... all in all, a bit a of minefield.
I'm hoping that with the development system it will allow GCC to be build correctly from the original source.