Fix implicit-fallthrough warnings in tst-setjmp.c

[Florian Weimer]

* Joseph Myers:

> diff --git a/setjmp/tst-setjmp.c b/setjmp/tst-setjmp.c
> index e83e896ebe..b377393ecf 100644
> --- a/setjmp/tst-setjmp.c
> +++ b/setjmp/tst-setjmp.c
> @@ -22,7 +22,7 @@
>  static jmp_buf env;
>  static int last_value = -1, lose = 0;
>  
> -static void
> +static __attribute__ ((__noreturn__)) void
>  jump (int val)
>  {
>    longjmp (env, val);

I think this patch is okay to push.