Every measurement repeats until a stated interval has passed, so a clock
that reads the same value twice does not slow the benchmark down, it stops
it returning at all.
CLOCK_MONOTONIC does not advance on every target. On qemu-intel64 it
reports success and stays at zero, while CLOCK_REALTIME advances normally,
and the benchmark spins in its first measurement with no output after the
heading.
Sample each candidate twice around a busy wait and take the first one whose
reading changes. Where none does, say so and skip the timing rather than
hang.
Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>
f4d71b6074