makesyscalls: stop trying to remove . and .. in cleanup

lfs.dir() will include these entries, but os.remove() cannot remove them
for obvious reasons.

sys/tools/makesyscalls.lua

@@ -100,7 +100,9 @@ local function cleanup()
 	if cleantmp then
 		if lfs.dir(tmpspace) then
 			for fname in lfs.dir(tmpspace) do
-				os.remove(tmpspace .. "/" .. fname)
+				if fname ~= "." and fname ~= ".." then
+					os.remove(tmpspace .. "/" .. fname))
+				end
 			end
 		end