[LTP] nanosleep: use POSIX runtime detection for CLOCK_MONOTONIC

[linuxtestproject.agent@gmail.com]

Hi Andrea,

On 2026-04-16, Andrea Cervesato wrote:
> nanosleep: use POSIX runtime detection for CLOCK_MONOTONIC

> +static inline clockid_t get_supported_clock(void)
> +{
> +#ifdef _POSIX_MONOTONIC_CLOCK
> +	if (_POSIX_MONOTONIC_CLOCK > 0)
> +		return CLOCK_MONOTONIC;
> +
> +	if (!_POSIX_MONOTONIC_CLOCK && sysconf(_SC_MONOTONIC_CLOCK) > 0)
> +		return CLOCK_MONOTONIC;
> +#endif
> +
> +	printf("CLOCK_MONOTONIC unavailable, test may fail due to "
> +	       "external clock adjustments\n");
> +	return CLOCK_REALTIME;
> +}

Correct POSIX runtime detection — handles all three _POSIX_MONOTONIC_CLOCK
states (>0, ==0, undefined) properly, and the unistd.h include in helpers.h
closes the silent fallback that affected 1-1.c, 2-1.c, and 10000-1.c.

Reviewed-by: LTP AI Reviewer <ltp-ai@noreply.github.com>

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