ego now builds and is used.

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.

util/ego/descr/build.lua

@@ -0,0 +1,30 @@
+local installmap = {}
+
+local function build_descr(name)
+	local descr = normalrule {
+		name = name,
+		ins = {
+			"lang/cem/cpp.ansi+cpp",
+			"./"..name..".descr",
+			"./descr.sed",
+			matching(filenamesof("modules/src/em_data+lib"), "em_mnem%.h$"),
+		},
+		outleaves = { name..".descr" },
+		commands = {
+			"%{ins[1]} -P -I%{dirname(ins[4])} %{ins[2]} > %{dir}/temp",
+			"sed -f %{ins[3]} < %{dir}/temp > %{outs}"
+		}
+	}
+
+	installmap["$(PLATIND)/ego/"..name..".descr"] = descr
+end
+
+build_descr("i386")
+build_descr("i86")
+build_descr("m68020")
+
+installable {
+	name = "pkg",
+	map = installmap
+}
+