libpthread removal in 2.34

[Florian Weimer]

* Adhemerval Zanella:

> I can help you on the libpthread removal project, if you want help on work
> besides review you can lay out the missing interfaces and work work in
> parallel.

I think we should probably swap between reviews and writing patches.
Splitting up the work seems hard because of the Makefile and Versions
conflicts that are difficult to avoid.  I have an abilist merger, which
should at least help with incorporating symbol additions due to
unrelated glibc work.

I have a bunch of pending patches in Patchwork right now.  The next step
after that will be moving the cancellation implementation, then
mutex/condvar (probably in one big patch).  I had started on the
mutex/condvar step before, but ran into unwinding interactions (hence
the present series) and the private-futex issue.  All this should cut
down struct pthread_functions by quite a bit.

Removing the $(pthread-compat-wrappers) seems largely independent of
that.  These symbols sort separately in the Versions file, too.  If you
could work on that, it would definitely help.  I suggest to follow the
one-commit-per-file approach, in case we need to track down regressions.
(My present series already removes longjmp.)

Thanks,
Florian