cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations sched/sched_setscheduler.c -o sched/sched_setscheduler -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
sched/sched_setscheduler.c:6:54: error: use of undeclared identifier 'sched_setscheduler'
int (*foo)(pid_t, int, const struct sched_param *) = sched_setscheduler;
                                                     ^
1 error generated.