When Perl "kill(9, ...)" fails, try "pg_ctl kill".

Per buildfarm member jacana, the former fails under msys Perl 5.8.8.
Back-patch to 9.6, like the code in question.

Discussion: https://postgr.es/m/GrdLgAdUK9FdyZg8VIcTDKVOkys122ZINEb3CjjoySfGj2KyPiMKTh1zqtRp0TAD7FJ27G-OBB3eplxIB5GhcQH5o8zzGZfp0MuJaXJxVxk=@yesql.se

src/test/perl/PostgresNode.pm

@@ -734,7 +734,9 @@ sub kill9
 	my $name = $self->name;
 	return unless defined $self->{_pid};
 	print "### Killing node \"$name\" using signal 9\n";
-	kill(9, $self->{_pid}) or BAIL_OUT("kill(9, $self->{_pid}) failed");
+	# kill(9, ...) fails under msys Perl 5.8.8, so fall back on pg_ctl.
+	kill(9, $self->{_pid})
+	  or TestLib::system_or_bail('pg_ctl', 'kill', 'KILL', $self->{_pid});
 	$self->{_pid} = undef;
 	return;
 }