Add MacPorts support to src/test/ldap tests.

Previously the test knew how to find an OpenLDAP installation at the
paths used by Homebrew.  Add the MacPorts paths too.

Author: Thomas Munro
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/CA%2BhUKGKrjGS7sO4jc53gp3qipCtEvThtdP_%3DzoixgX5ZBq4Nbw%40mail.gmail.com

src/test/ldap/README

@@ -49,4 +49,4 @@ and net/openldap24-server.)
 macOS: We do not recommend trying to use the Apple-provided version of
 OpenLDAP; it's very old, plus Apple seem to have changed the launching
 conventions for slapd.  The paths in the test file are set on the
-assumption that you installed OpenLDAP using Homebrew.
+assumption that you installed OpenLDAP using Homebrew or MacPorts.

src/test/ldap/t/001_auth.pl

@@ -17,11 +17,18 @@ my ($slapd, $ldap_bin_dir, $ldap_schema_dir);
 
 $ldap_bin_dir = undef;    # usually in PATH
 
-if ($^O eq 'darwin')
+if ($^O eq 'darwin' && -d '/usr/local/opt/openldap')
 {
+	# typical paths for Homebrew
 	$slapd           = '/usr/local/opt/openldap/libexec/slapd';
 	$ldap_schema_dir = '/usr/local/etc/openldap/schema';
 }
+elsif ($^O eq 'darwin' && -d '/opt/local/etc/openldap')
+{
+	# typical paths for MacPorts
+	$slapd           = '/opt/local/libexec/slapd';
+	$ldap_schema_dir = '/opt/local/etc/openldap/schema';
+}
 elsif ($^O eq 'linux')
 {
 	$slapd           = '/usr/sbin/slapd';