pgsql: Fix gai_strerror() thread-safety on Windows.

Fix gai_strerror() thread-safety on Windows.

Commit 5579388d removed code that supplied a fallback implementation of
getaddrinfo(), which was dead code on modern systems. One tiny piece of
the removed code was still doing something useful on Windows, though:
that OS's own gai_strerror()/gai_strerrorA() function returns a pointer
to a static buffer that it overwrites each time, so it's not
thread-safe. In rare circumstances, a multi-threaded client program
could get an incorrect or corrupted error message.

Restore the replacement gai_strerror() function, though now that it's
only for Windows we can put it into a win32-specific file and cut it
down to the errors that Windows documents. The error messages here are
taken from FreeBSD, because Windows' own messages seemed too verbose.

Back-patch to 16.

Reviewed-by: Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>
Discussion: https://postgr.es/m/CA%2BhUKGKz%2BF9d2PTiXwfYV7qJw%2BWg2jzACgSDgPizUw7UG%3Di58A%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/65f438471b769f6b9706a386028f81df065d0a25

Modified Files
--------------
configure | 6 +++++
configure.ac | 1 +
src/include/port/win32/sys/socket.h | 8 +++++++
src/port/meson.build | 1 +
src/port/win32gai_strerror.c | 45 +++++++++++++++++++++++++++++++++++++
5 files changed, 61 insertions(+)