Wasn't exporting the plat headers; refactor to make this a little cleaner.

plat/linux386/include/build.lua

@@ -0,0 +1,24 @@
+include("plat/build.lua")
+
+headermap = {}
+packagemap = {}
+
+local function addheader(h)
+	headermap[h] = "./"..h
+	packagemap["$(PLATIND)/linux386/include/"..h] = "./"..h
+end
+
+addheader("ack/config.h")
+addheader("sys/ioctl.h")
+addheader("unistd.h")
+
+acklibrary {
+	name = "headers",
+	hdrs = headermap
+}
+
+installable {
+	name = "pkg",
+	map = packagemap
+}
+