Cygwin: mknod: disable creating special files on NFS

This simply doesn't work (yet?) but leaves unusable files behind.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/syscalls.cc

@@ -3292,6 +3292,12 @@ mknod (const char *path, mode_t mode, dev_t dev)
 	  __leave;
 	}
 
+      if (w32path.fs_is_nfs ())
+	{
+	  set_errno (EPERM);
+	  __leave;
+	}
+
       return mknod_worker (w32path, mode, major, minor);
     }
   __except (EFAULT)