[RFC PATCH glibc] Linux: Use fixed rseq_len value for rseq registration

[Florian Weimer]

* Mathieu Desnoyers:

> +  /* The rseq_len parameter does not allow extending struct rseq.  Fix its
> +     value to 32 as expected by the Linux kernel.  */
> +  ret = INTERNAL_SYSCALL_CALL (rseq, &__rseq_abi, 32, 0, RSEQ_SIG);

If the layout of struct rseq can change in the kernel headers, than far
more significant changes are needed.  glibc cannot change its ABI
depending on the version of the kernel headers it is compiled against.

Thanks,
Florian