cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration time/timer_settime.c -o time/timer_settime -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
time/timer_settime.c:26:19: error: use of undeclared identifier 'SIGEV_SIGNAL'
                .sigev_notify = SIGEV_SIGNAL,
                                ^
time/timer_settime.c:24:18: error: variable has incomplete type 'struct sigevent'
        struct sigevent event =
                        ^
time/timer_settime.c:24:9: note: forward declaration of 'struct sigevent'
        struct sigevent event =
               ^
time/timer_settime.c:31:7: error: call to undeclared function 'timer_create'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        if ( timer_create(CLOCK_MONOTONIC, &event, &timer) < 0 )
             ^
time/timer_settime.c:34:7: error: call to undeclared function 'timer_settime'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        if ( timer_settime(timer, 0, &its, NULL) < 0 )
             ^
4 errors generated.