Sort record fields in lin definitions

Fixes #102

testsuite/canonical/gold/FoodsFin.gf

@@ -99,4 +99,4 @@ lin Expensive =
                            ResFin_NPossIllat ParamX_Pl => "kalliisii";
                            ResFin_NCompound => "kallis"}};
          hasPrefix = Prelude_False; p = ""};
-}
+}