cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration sched/sched_getscheduler.c -o sched/sched_getscheduler -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
sched/sched_getscheduler.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);
                     ^
1 error generated.