Обсуждение: pgsql: Sync our copy of the timezone library with IANA releasetzcode20

Sync our copy of the timezone library with IANA release tzcode2018g.

This patch absorbs an upstream fix to "zic" for a recently-introduced
bug that made it output data that some 32-bit clients couldn't read.
Given the current source data, the bug only manifests in zones with
leap seconds, which we don't generate, so that there's no actual
change in our installed timezone data files from this.  Still, in
case somebody uses our copy of "zic" to do something else, it seems
best to apply the fix promptly.

Also, update the README's notes about converting upstream code to
our conventions.

Branch
------
REL_10_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/48c6df11a434765b1154dc07803bf95e764632fb

Modified Files
--------------
src/timezone/README | 12 +++++++--
src/timezone/zic.c  | 74 ++++++++++++++++++++++++++++-------------------------
2 files changed, 49 insertions(+), 37 deletions(-)