pom: Cache tzdata before entering capability mode

Pom uses localtime() so needs tzdata available.

PR: 278574
Reported by: Tatsuki Makino
Reviewed by: ivy
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51521

(cherry picked from commit 0fde36fe04b2b656a2215f7dad07a52884e8dcfd)
(cherry picked from commit 05459c1b860c086ada0cacb398fa5d61a240e0ca)