is used only by the X server, and should be grouped there. Later we may
also add unconditional install of the source-form "rgb.txt", usable by all
programs, into xbase.
This allows the xbase set to be shared between the mipsel platforms, and all
m68k platforms except atari (which has additional XF86 add-ons).
* factor all m68k common stuff into lists/*/ad.m68k
XXX: this should be done for mips (when it's not just the pmax), and
powerpc (when there's a powerpc port put here ...)