Skip some permissions checks on Cygwin

These are checks that are already skipped on other Windows systems.

Backpatch to all live branches, as appropriate.

src/bin/initdb/t/001_initdb.pl

@@ -77,7 +77,7 @@ command_fails([ 'initdb', $datadir ], 'existing data directory');
 SKIP:
 {
 	skip "unix-style permissions not supported on Windows", 2
-	  if ($windows_os);
+	  if ($windows_os || $Config::Config{osname} eq 'cygwin');
 
 	# Init a new db with group access
 	my $datadir_group = "$tempdir/data_group";

src/bin/pg_basebackup/t/010_pg_basebackup.pl

@@ -218,7 +218,8 @@ SKIP:
 # skip on Windows.
 SKIP:
 {
-	skip "symlinks not supported on Windows", 18 if ($windows_os);
+	skip "symlinks not supported on Windows", 18
+	  if ($windows_os);
 
 	# Move pg_replslot out of $pgdata and create a symlink to it.
 	$node->stop;
@@ -304,9 +305,15 @@ SKIP:
 		"tablespace symlink was updated");
 	closedir $dh;
 
-	# Group access should be enabled on all backup files
+	SKIP:
-	ok(check_mode_recursive("$tempdir/backup1", 0750, 0640),
+	{
-		"check backup dir permissions");
+		skip "unix-style permissions not supported on Windows", 1
+		  if ($Config::Config{osname} eq 'cygwin');
+
+		# Group access should be enabled on all backup files
+		ok(check_mode_recursive("$tempdir/backup1", 0750, 0640),
+		   "check backup dir permissions");
+	}
 
 	# Unlogged relation forks other than init should not be copied
 	my ($tblspc1UnloggedBackupPath) =

src/bin/pg_ctl/t/001_start_stop.pl

@@ -78,7 +78,8 @@ $logFileName = "$tempdir/data/perm-test-640.log";
 
 SKIP:
 {
-	skip "group access not supported on Windows", 3 if ($windows_os);
+	skip "group access not supported on Windows", 3
+	  if ($windows_os || $Config::Config{osname} eq 'cygwin');
 
 	system_or_bail 'pg_ctl', 'stop', '-D', "$tempdir/data";
 

src/bin/pg_rewind/t/002_databases.pl

@@ -57,7 +57,7 @@ template1
   SKIP:
 	{
 		skip "unix-style permissions not supported on Windows", 1
-		  if ($windows_os);
+		  if ($windows_os || $Config::Config{osname} eq 'cygwin');
 
 		ok(check_mode_recursive($node_master->data_dir(), 0750, 0640),
 			'check PGDATA permissions');