see also https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=235327
The current port does this:
cd /usr/local/libexec
ls -l mod_passenger.so
mod_passenger.so -> ../../ruby/gems/2.4/gems/passenger-6.0.0/buildout/apache2/mod_passenger.so
That link should be ../../lib/ruby/gems/2.4/gems/passenger-6.0.0/buildout/apache2/mod_passenger.so
I tried ${RLN}, it also gets it wrong.
Using ${LN} gets this working