No it's awful. They are most certainly not up to date, and even worse, the compilers they ship that advertise certain flags aren't even necessarily feature complete. A glaring example of this was the lack of thread_local support for ages.
Yup. It was only about a year ago that the undefined behaviour sanitizer stopped segfaulting when I turned it on, despite it being clearly "documented" in the man page. I'm amazed that a company with the resources of Apple has such shoddy developer tools.