cc -pthread  -Wall -Wextra -Werror=implicit-function-declaration signal/pthread_kill.c -o signal/pthread_kill -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt -lintl -liconv
signal/pthread_kill.c: In function ‘main’:
signal/pthread_kill.c:40:23: error: implicit declaration of function ‘pthread_kill’; did you mean ‘pthread_self’? [-Wimplicit-function-declaration]
   40 |         if ( (errno = pthread_kill(thread, SIGUSR1)) < 0 )
      |                       ^~~~~~~~~~~~
      |                       pthread_self