Fix build on 12.0-CURRENT

iohyve.8.gz is never created with NO_BUILD=yes set and the build fails
with:

> Staging for iohyve-0.7.9

> Generating temporary packing list

...
install -c iohyve.8.gz /wrkdirs/usr/ports/sysutils/iohyve/work/stage//usr/local/man/man8/
install: iohyve.8.gz: No such file or directory

• Error code 71

PR: 220624
Approved by: lme (mentor, maintainer)
MFH: 2017Q3