[tile] support openat() in not-cancel.h

[Roland McGrath]

>  /* Uncancelable versions of cancelable interfaces.  Linux version.
> -   Copyright (C) 2003, 2006 Free Software Foundation, Inc.
> +   Copyright (C) 2003, 2006, 2011 Free Software Foundation, Inc.

It's 2012.

>  #include <sys/types.h>
>  #include <sysdep.h>
> +#ifndef __NR_open
> +# include <fcntl.h>
> +#endif

It's probably easier all around on maintenance not to conditionalize this
#include.  It doesn't hurt to have it when it's not needed.

> +# error "Neither __NR_open nor __NR_openat available."

s/available/is &/


Thanks,
Roland