ldap tests: Don't run on unsupported operating systems.

The tests currently fail on unsupported operating systems, rather than getting
skipped. The ony reason this doesn't cause problems is that the tests aren't
run by default.

Discussion: https://postgr.es/m/721828a7-3043-6803-a85b-da63538db3cc@enterprisedb.com

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

@@ -6,17 +6,18 @@ use warnings;
 use PostgreSQL::Test::Utils;
 use PostgreSQL::Test::Cluster;
 use Test::More;
+use Config;
 
-if ($ENV{with_ldap} ne 'yes')
-{
-	plan skip_all => 'LDAP not supported by this build';
-}
 
 my ($slapd, $ldap_bin_dir, $ldap_schema_dir);
 
 $ldap_bin_dir = undef;    # usually in PATH
 
-if ($^O eq 'darwin' && -d '/usr/local/opt/openldap')
+if ($ENV{with_ldap} ne 'yes')
+{
+	plan skip_all => 'LDAP not supported by this build';
+}
+elsif ($^O eq 'darwin' && -d '/usr/local/opt/openldap')
 {
 	# typical paths for Homebrew
 	$slapd           = '/usr/local/opt/openldap/libexec/slapd';
@@ -39,6 +40,10 @@ elsif ($^O eq 'freebsd')
 	$slapd           = '/usr/local/libexec/slapd';
 	$ldap_schema_dir = '/usr/local/etc/openldap/schema';
 }
+else
+{
+	plan skip_all => "ldap tests not supported on $^O or dependencies not installed";
+}
 
 # make your own edits here
 #$slapd = '';