This needed lots of refactoring to ego --- not all platforms have ego descr
files, and ego will just crash if you invoke it without one. I think originally
it was never intended that these platforms would be used at -O2 or above.
Plats now only specify the ego descr file if they have one.
directories --- wrangling descr files was too hard. C programs can be built
for cpm, pc86, linux386, linux68k!
--HG--
branch : dtrg-buildsystem
rename : util/ack/build.mk => util/led/build.mk
rename : util/LLgen/build.mk => util/topgen/build.mk
