POSIX requires that when you claim _POSIX_CPUTIME and _POSIX_THREAD_CPUTIME,
not only the clock_* calls but also timer_* calls must support the thread
and process CPU time clocks. This patch provides that support, building on
my recent additions to support these clocks in the POSIX clock_* interfaces.
This patch will not work without those changes, as well as the patch fixing
the timer lock-siglock deadlock problem.
The apparent pervasive changes to posix-timers.c are simply that some
fields of struct k_itimer have changed name and moved into a union.
This was appropriate since the data structures required for the existing
real-time timer support and for the new thread/process CPU-time timers are
quite different.