textproc/source-highlight: Add --with-boost

Otherwise, it fails to find Boost.Regex when LOCALBASE is not
/usr/local.

PR: 288761
Reviewed by: arrowd
Approved by: arrowd (ports), maintainer (timeout, 9 months)
Differential Revision: https://reviews.freebsd.org/D57125

(cherry picked from commit 20ee6d87ee7a74a8a843e393ed03146736506839)