When compiling kernel with SMP disabled, the build warns with:
kernel/sched/core.c: In function âupdate_rq_clock_taskâ:
kernel/sched/core.c:139:17: warning: unused variable âirq_deltaâ [-Wunused-variable]
s64 steal = 0, irq_delta = 0;
Fix this by revert the HAVE_SCHED_AVG_IRQ to
defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
Fixes: 2e62c4743adc ("sched/fair: Remove #ifdefs from scale_rt_capacity()")