/x        Includes false conditionals in listing

          If a conditional IF, IFNDEF, IFDEF, and so forth evaluates to
          false, the /x option causes the statements inside the
          conditional block to appear in the listing file. This option
          also causes the conditional directives themselves to be listed;
          normally they are not.

          You must specify a listing file on the command line or via the
          /l option, otherwise /x has no effect.