[PATCH] x86_64/clone.S: Upate comments

[Florian Weimer]

* H. J. Lu via Libc-alpha:

>     The parameters are passed in register and on the stack from userland:
>     rdi: fn
>     rsi: child_stack
>     rdx:	flags
>     rcx: arg
> +    r8:	TID field in parent
> +    r9: thread pointer
> +%rsp+8:	TID field in child

I don't get the pattern of the column alignment here, but the patch is
an improvement, so please push it.

Thanks,
Florian