{opt}_CMAKE_ARGS_ON isn't a valid syntax. Use {opt}_CMAKE_ON instead.
This makes the soci port obey the FIREBIRD option (otherwise it always
looks for Firebird, even when you don't want it to).

Submitted by yuri@ in PR 209530, maintainer timeout (17 months).

PR: 209530
Submitted by: yuri@FreeBSD.org
Reviewed by: yuri (submitter)
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D12919