cc -O2 -pipe  -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 
semaphore/sem_clockwait.c:17:7: error: call to undeclared function 'sem_clockwait'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
   17 |         if ( sem_clockwait(&sem, CLOCK_MONOTONIC, &long_timeout) < 0 )
      |              ^
1 error generated.