cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration sched/sched_rr_get_interval.c -o sched/sched_rr_get_interval -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
sched/sched_rr_get_interval.c:14:7: error: call to undeclared function 'sched_rr_get_interval'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        if ( sched_rr_get_interval(0, &ts) < 0 )
             ^
1 error generated.