cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration pthread/pthread_rwlock_clockrdlock.c -o pthread/pthread_rwlock_clockrdlock -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
pthread/pthread_rwlock_clockrdlock.c:16:16: error: call to undeclared function 'pthread_rwlock_clockrdlock'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
   16 |         if ( (errno = pthread_rwlock_clockrdlock(&rwlock, CLOCK_MONOTONIC,
      |                       ^
1 error generated.