One of patches (rxvt-unicode-9.19-secondary-wheel.patch) modify man page source file rxvt.1.pod, but `make alldoc` isn't executed and thus doesn't regenerate rxvt.1.man.in used to make final rxvt.1.man. This require `pod2man` command, which means extra dependency on virtual/perl-podlators.
Fixed in -r2. USE=vanilla is gone.