afed3ce removed the sys/unix package and moved over to sys/posix, it has
new bindings for the pthread APIs but should have been equivalent (not).
8fb7182 used `CANCEL_ENABLE :: 0`, `CANCEL_DISABLE :: 1`, `CANCEL_DEFERRED :: 0`, `CANCEL_ASYNCHRONOUS :: 1` for Darwin, while the
correct values are `1`, `0`, `2` and `0` respectively (same mistake was made for
FreeBSD in that commit).
What this meant is that the
`pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS)` was not actually
successful, but because the error wasn't checked it was assumed it was.
It also meant `pthread_setcancelstate(PTHREAD_CANCEL_ENABLE)` would
actually be setting `PTHREAD_CANCEL_DISABLE`.
The code in this PR restores the behaviour by now actually deliberately
setting `PTHREAD_CANCEL_DISABLE` and not setting
`PTHREAD_CANCEL_ASYNCHRONOUS` which was the previous behaviour that does
actually seem to work for some reason.
(I also fixed an issue in fmt where `x` would use uppercase if it was a
pointer.)
