cc -pipe -O   -pthread  -Wall -Wextra -Werror=implicit-function-declaration semaphore/sem_clockwait.c -o semaphore/sem_clockwait -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread -lrt  -lrt -lcrypt
semaphore/sem_clockwait.c: In function 'main':
semaphore/sem_clockwait.c:17:7: error: implicit declaration of function 'sem_clockwait'; did you mean 'sem_timedwait'? [-Werror=implicit-function-declaration]
  if ( sem_clockwait(&sem, CLOCK_MONOTONIC, &long_timeout) < 0 )
       ^~~~~~~~~~~~~
       sem_timedwait
cc1: some warnings being treated as errors