MFC r339873:

MFC r339873:
 Set OPTIONS_UNSET in the argument list to env(1), and add
 AVAHI to the list.  This fixes the textproc/docproj build
 seemingly following FLAVORS being added.

 Specifically, the problem with the dependency chain here is:
 - textproc/docproj depends on print/cups, which sets AVAHI=on
   by default;
 - net/avahi-app depends on devel/gobject-introspection, which
   requires python3+;
 - graphics/netpbm depends on graphics/mesa-libs, which can
   only be built with python2.7;
 - textproc/docproj depends on a number of graphics ports for
   font rendering, etc.

MFC r339875:
 Pass _BRANCH in the reldoc target to ensure the correct
 src branch is used when generating the hardware.html page.

Approved by:	re (kib)
Sponsored by:	The FreeBSD Foundation