[tz] Add option to act like global-tz

[Paul Eggert]

On 8/16/22 00:08, Bradley White wrote:
> Is the intent that the standard install and the "PACKRATDATA=backzone
> PACKRATLIST=zone.tab" install should not exhibit any differences for 1970+
> timestamps?

Yes, and you can test this by running something like the following in a 
source directory. The diff command should output nothing. (The test 
takes a while.) I did this sort of test before releasing 2022b.

make clean
make TOPDIR=$PWD/tza ZFLAGS=-r at 0 install
./zdump -i $(awk '/^[^#]/{print $3}' zone1970.tab) >a.tzs
make clean
make TOPDIR=$PWD/tzb ZFLAGS=-r at 0 \
   PACKRATDATA=backzone PACKRATLIST=zone.tab \
   install
./zdump -i $(awk '/^[^#]/{print $3}' zone1970.tab) >b.tzs
diff a.tzs b.tzs
rm -r tza tzb a.tzs b.tzs