pgsql: Handle SIGTERM in pg_receivewal and pg_recvlogical

Handle SIGTERM in pg_receivewal and pg_recvlogical

In pg_receivewal, compressed output is only flushed on clean exits. The
reason to support SIGTERM as well as SIGINT (which is currently handled)
is that pg_receivewal might well be running as a daemon, and systemd's
default KillSignal is SIGTERM.

Since pg_recvlogical is also supposed to run as a daemon, teach it about
SIGTERM as well and update the documentation to match. While in there,
change pg_receivewal's time_to_stop to be sig_atomic_t like it is in
pg_recvlogical.

Author: Christoph Berg <myon(at)debian(dot)org>
Reviewed-by: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/Yvo/5No5S0c4EFMj(at)msg(dot)df7cb(dot)de

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/8b60db774356117fab2eb53fb37160fa3e173cdb

Modified Files
--------------
doc/src/sgml/ref/pg_receivewal.sgml | 8 +++++---
doc/src/sgml/ref/pg_recvlogical.sgml | 18 ++++++++++++++++++
src/bin/pg_basebackup/pg_receivewal.c | 11 ++++++-----
src/bin/pg_basebackup/pg_recvlogical.c | 9 +++++----
4 files changed, 34 insertions(+), 12 deletions(-)