Make zoneinfo optional so that a filesystem upgrade/update does not overwrite

possibly installed thirdparte zoneinfo databases (from ports for example).

PR:		bin/104713
Submitted by:	Mark Andrews <Mark_Andrews at isc dot org> (original patch
		rewritten by me to be more consistent with the new practise).
Approved by: 	re (kensmith)
Approved by:	imp (mentor)
Reviewed by:	ru (some time ago already)

share/Makefile

@@ -25,7 +25,7 @@ SUBDIR=	${_colldef} \
 	tabset \
 	termcap \
 	${_timedef} \
-	zoneinfo
+	${_zoneinfo}
 
 .if ${MK_LOCALES} != "no"
 _colldef =	colldef
@@ -68,4 +68,8 @@ _sendmail=	 sendmail
 _doc=		doc
 .endif
 
+.if ${MK_ZONEINFO} != "no"
+_zoneinfo=	zoneinfo
+.endif
+
 .include <bsd.subdir.mk>

share/mk/bsd.own.mk

@@ -358,6 +358,7 @@ WITH_IDEA=
     TOOLCHAIN \
     USB \
     WPA_SUPPLICANT_EAPOL \
+    ZONEINFO \
     ZFS
 .if defined(WITH_${var}) && defined(WITHOUT_${var})
 .error WITH_${var} and WITHOUT_${var} can't both be set.