* Add StdcppWaiter to the end of the list of waiter implementations

Since ABSL_INTERNAL_HAVE_STDCPP_WAITER is defined on all systems
it is effectively a fallback. I left the condition there in case
we have to disable it on some platform in the future.

PiperOrigin-RevId: 555629066
Change-Id: I76ca78c7f36d1d02dc4950a44c66903a2aaf2a52

* Use native methods to implement absl::base_internal::GetPID() on
FreeBSD, NetBSD, and OpenBSD

https://man.freebsd.org/cgi/man.cgi?query=pthread_getthreadid_np
https://man.netbsd.org/_lwp_self.2
https://man.openbsd.org/getthrid.2

* Abseil LTS branch, Aug 2023, Patch 1
Bump ABSL_LTS_RELEASE_PATCH_LEVEL to 1