cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration sched/sched_setscheduler.c -o sched/sched_setscheduler -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
sched/sched_setscheduler.c:10:15: error: call to undeclared function 'sched_getscheduler'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        int policy = sched_getscheduler(0);
                     ^
sched/sched_setscheduler.c:18:7: error: call to undeclared function 'sched_getparam'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        if ( sched_getparam(0, &params) < 0 )
             ^
sched/sched_setscheduler.c:24:7: error: call to undeclared function 'sched_setscheduler'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        if ( sched_setscheduler(0, policy, &params) < 0 )
             ^
3 errors generated.