Added '--with-x11' option.

As a followup of #14564 and #14564, `ghostcript` 9.06 works fine for me with a properly set dependency on recent XQuartz, as in the `gv` formula. This solves #16865 as long as `ghostscript` is compiled with the `with-x11` option. We'll have to wait for #14456 in order to modify the `gv` formula to make that check explicit.