implement smaller than comparison

which is NOT an operator in the risc sense
rather a minus and a check for sign
(which _could be more efficient in arm, with conditional execution)

test/risc/builtin/test_simple_int.rb

@@ -31,7 +31,7 @@ module Risc
       end
       def test_smaller
         run_all "4 < 5"
-        assert_equal 16 , get_return.value
+        assert_equal Parfait::TrueClass , get_return.class
       end
     end
   end