pkg-message currently states the advice to add WITH_MPM=event
if its build by poudriere and with ZTS option enabled.
This is also true if Synth is used, therefore adding it.
Reported by: Dennis <denradford@gmail.com>
The message should point to a common mistake, when building
lang/php71 with ZTS option enabled using poudriere.
There is already the same message in lang/php70.
Reported by: Jim Trigg <jktrigg@gmail.com>
