Cygwin: FIFO: use FILE_PIPE_REJECT_REMOTE_CLIENTS flag

Add that flag to the pipe type argument when creating the Windows
named pipe.  And add a definition of that flag to ntdll.h (copied from
/usr/include/w32api/ddk/ntifs.h).

winsup/cygwin/fhandler_fifo.cc

@@ -184,7 +184,8 @@ fhandler_fifo::create_pipe_instance (bool first)
   timeout.QuadPart = -500000;
   status = NtCreateNamedPipeFile (&ph, access, &attr, &io, sharing,
 				  first ? FILE_CREATE : FILE_OPEN, 0,
-				  FILE_PIPE_MESSAGE_TYPE,
+				  FILE_PIPE_MESSAGE_TYPE
+				    | FILE_PIPE_REJECT_REMOTE_CLIENTS,
 				  FILE_PIPE_MESSAGE_MODE,
 				  nonblocking, max_instances,
 				  DEFAULT_PIPEBUFSIZE, DEFAULT_PIPEBUFSIZE,

winsup/cygwin/ntdll.h

@@ -557,7 +557,8 @@ enum
 enum
 {
   FILE_PIPE_BYTE_STREAM_TYPE = 0,
-  FILE_PIPE_MESSAGE_TYPE = 1
+  FILE_PIPE_MESSAGE_TYPE = 1,
+  FILE_PIPE_REJECT_REMOTE_CLIENTS = 2
 };
 
 typedef struct _FILE_PIPE_PEEK_BUFFER {