localtime.c is a stripped-down version of that from tzcode2007k, from
ftp://elsie.nci.nih.gov/pub/.  Apart from removing unused code and
merging in the parts of private.h which are needed, the main changes
are

- to use environment variable TZDIR to point to the zoneinfo files, and
  failing that, R_HOME/share/zoneinfo.

- to call getTZinfo() to get the default timezone if TZ is unset.


zoneinfo.zip was formed by installing tzcode/tzdata on x86_64 Linux,
and zipping up the results, after adding a file VERSION giving the
version.  It should be possible to build the compiled databases on
Windows, but zic.c assumes links and so would need a lot of work.
(It look like the binary databases are byte streams, and so do not
depend on the architecture.  There are some comments about whether
time_t is signed, which it is on all sensible platforms.)

To remake it, use a machine with zic in the path (it may be /usr/sbin/zic).
Copy the current version of tzdataXXX.tar.gz to this directory and run

make -f Make.zi VERSION=2007k

for the appropriate version.