illumos gate

We don't actually have a mandoc macro set yet, sadly. Maybe file a bug and integrate one?
(I don't know enough to know if one from a BSD could be added and be compatible with our man, and roff.)

So, this will work for some people and not for others because man(1) is sensitive to $PATH where it arguable shouldn't be:

If /usr/gnu/bin is ahead of /usr/bin in your path, your nroff will be groff, and -mandoc will be present and functional.
If it is not, nroff will be our nroff, -mandoc won't be present, and the mandoc page won't render.

man depends on groff to provide gpic, which makewhatis uses, but nothing is done to cause man to use groff (and historically, it's used our nroff instead).