If a port modifies OPTIONS_UNSET after including bsd.port.options.mk
then these values were wrong even though all of 'showconfig',
'pretty-print-config', and the package generated all had the expected
Only Poudriere and synth use these variables for incremental build checks.
My initial thoughts were that the print/ghostscript9-agpl-base/files/Makefile.drivers_post
file is wrong for modifying OPTIONS this late but the fact that all
other options printers and the package work as the port expects makes
me accept it.
The alternative to using bmake :@ here would be to move the existing
code to bsd.port.mk at the end of the pre-check-config block.