[PATCH v3 0/6] nptl: Fix pthread_cond_signal missing a sleeper

[malteskarupke@fastmail.fm]

The first patch in this series fixes BZ 25847, the remaining patches
do follow-up clean-up work.

-- New in v3:
Fixed that the first patch didn't work on its own. It had a bug that
was fixed in the third patch in the series. Now the series can be
partially applied and it's fine to stop after any patch.

Also rebased the patches to work on top of 2.36/master

-- New in v2:
The first patch now has the calls at the end of pthread_cond_wait in
the right order.

The third patch now clears the wake-request flag correctly, removing a
case where a waiter could write to a condvar after it was destroyed.

The fifth patch now renames wrefs to crefs.

I also updated comments as requested.

Finally I added another patch because I realized that g1_start was too
complex for its reduced role after signal stealing was no longer
possible, so the final patch cleans that up.