Ignore more environment variables in pg_regress.c

This is similar to the work done in 8279f68 for TestLib.pm, where
environment variables set may cause unwanted failures if using a
temporary installation with pg_regress.  The list of variables reset is
adjusted in each stable branch depending on what is supported.

Comments are added to remember that the lists in TestLib.pm and
pg_regress.c had better be kept in sync.

Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/YMNR9GYDn+fHlMta@paquier.xyz
Backpatch-through: 9.6

src/test/perl/TestLib.pm

@@ -63,6 +63,7 @@ BEGIN
 	delete $ENV{LC_ALL};
 	$ENV{LC_MESSAGES} = 'C';
 
+	# This list should be kept in sync with pg_regress.c.
 	my @envkeys = qw (
 	  PGCLIENTENCODING
 	  PGCONNECT_TIMEOUT

src/test/regress/pg_regress.c

@@ -802,14 +802,33 @@ initialize_environment(void)
 		 * we also use psql's -X switch consistently, so that ~/.psqlrc files
 		 * won't mess things up.)  Also, set PGPORT to the temp port, and set
 		 * PGHOST depending on whether we are using TCP or Unix sockets.
+		 *
+		 * This list should be kept in sync with TestLib.pm.
 		 */
-		unsetenv("PGDATABASE");
-		unsetenv("PGUSER");
-		unsetenv("PGSERVICE");
-		unsetenv("PGSSLMODE");
-		unsetenv("PGREQUIRESSL");
+		/* PGCLIENTENCODING, see above */
 		unsetenv("PGCONNECT_TIMEOUT");
 		unsetenv("PGDATA");
+		unsetenv("PGDATABASE");
+		unsetenv("PGGSSENCMODE");
+		unsetenv("PGGSSLIB");
+		/* PGHOSTADDR, see below */
+		unsetenv("PGKRBSRVNAME");
+		unsetenv("PGPASSFILE");
+		unsetenv("PGPASSWORD");
+		unsetenv("PGREQUIREPEER");
+		unsetenv("PGREQUIRESSL");
+		unsetenv("PGSERVICE");
+		unsetenv("PGSERVICEFILE");
+		unsetenv("PGSSLCERT");
+		unsetenv("PGSSLCRL");
+		unsetenv("PGSSLKEY");
+		unsetenv("PGSSLMODE");
+		unsetenv("PGSSLROOTCERT");
+		unsetenv("PGTARGETSESSIONATTRS");
+		unsetenv("PGUSER");
+		/* PGPORT, see below */
+		/* PGHOST, see below */
+
 #ifdef HAVE_UNIX_SOCKETS
 		if (hostname != NULL)
 			doputenv("PGHOST", hostname);