manual: add syscall list appendix

[DJ Delorie]

"Carlos O'Donell" <carlos@redhat.com> writes:
> $0.02. No. This is similar to the Linux kernel version checks. We should have a minimum
> and bump them up as we audit and review.

Then it needs to be recorded somewhere other than the configure line,
because 99.9% of all ./configure will not include it.

>> It's long for an appendix.  Do we have a chapter on cancellation?  Do we
>> want to be that Linux-centric?
>
> May you please expand on what you think is long for an appendix?

We're up to two long paragraphs about how glibc does syscalls, in
general, including cancellation.  Do we mention cancellation anywhere
else in the manual?  Do we have a chapter on how we wrap kernel-level
syscalls?  I'm thinking, is there enough information here to either move
the whole thing into a real chapter, or separate the big paragraphs from
the generated list?