pgsql: Sort out getpeereid() and peer auth handling on Windows

Sort out getpeereid() and peer auth handling on Windows

The getpeereid() uses have so far been protected by HAVE_UNIX_SOCKETS,
so they didn't ever care about Windows support.  But in anticipation
of Unix-domain socket support on Windows, that needs to be handled
differently.

Windows doesn't support getpeereid() at this time, so we use the
existing not-supported code path.  We let configure do its usual thing
of picking up the replacement from libpgport, instead of the custom
overrides that it was doing before.

But then Windows doesn't have struct passwd, so this patch sprinkles
some additional #ifdef WIN32 around to make it work.  This is similar
to existing code that deals with this issue.

Reviewed-by: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/5974caea-1267-7708-40f2-6009a9d653b0@2ndquadrant.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/f14413b684d57211068ee56ee04695efcc87a23a

Modified Files
--------------
configure                         | 36 +++++++++++++++---------------------
configure.in                      | 11 ++++-------
src/backend/libpq/auth.c          | 17 ++++++++---------
src/include/port.h                |  2 +-
src/interfaces/libpq/fe-connect.c | 10 +++++++---
src/tools/msvc/Mkvcbuild.pm       |  2 +-
6 files changed, 36 insertions(+), 42 deletions(-)