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

usr.bin/pom/pom.c

@@ -83,6 +83,7 @@ main(int argc, char **argv)
 		err(1, "unable to limit capabitilities for stdio");
 
 	caph_cache_catpages();
+	caph_cache_tzdata();
 	if (caph_enter() < 0)
 		err(1, "unable to enter capability mode");