selftests: timers: Measure the CPU timers on the clock they count

Commit b00385b8d081 ("selftests/posix_timers: Use CLOCK_THREAD_CPUTIME_ID
for ITIMER_PROF measurements") gave ITIMER_PROF the clock it counts, as
measuring a CPU timer against the wall says nothing on a machine where
the task does not have a CPU to itself. The other CPU timers are still
measured against CLOCK_REALTIME and fail the same way. With four busy
loops on the two CPUs of a test machine:

  not ok 2 ITIMER_VIRTUAL
  not ok 5 timer_create() per CLOCK_THREAD_CPUTIME_ID
  not ok 6 timer_create() per CLOCK_PROCESS_CPUTIME_ID

ITIMER_VIRTUAL counts the time the task spends in userspace, so take
CLOCK_THREAD_CPUTIME_ID for it as well; the loop it runs stays in
userspace, so what that clock adds for system time is far inside the
half a second the check allows. check_timer_create() arms its timer on
the clock it is given, so measure on that one.

The test then passes whole on that machine, 19 of 19, busy or idle.

Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20260917015237.2462954-2-eva.kurchatova@virtuozzo.com

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