[groff] Loss of MSVC support

[Doug McIlroy]

I run groff on windows a lot, but via cygwin, which emulates
Unix. I am inclined to think that if you like the groff toolset,
you are likely to want other Unix capability, too, and thus
gravitate towards facilities like cygwin.

I take it that Keith uses groff on bare Windows without a
Unix veneer. If many people work in that mode, we should not
abandon them.

Doug