/opt/IBM/openxlC/17.1.1/bin/ibm-clang -pthread  -Wall -Wextra -Werror=implicit-function-declaration sys_socket/accept4.c -o sys_socket/accept4 -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt -latomic
sys_socket/accept4.c:45:18: error: call to undeclared function 'accept4'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        int server_fd = accept4(listen_fd, (struct sockaddr*) &peer, &peer_len,
                        ^
sys_socket/accept4.c:45:18: note: did you mean 'naccept'?
/usr/include/sys/socket.h:640:9: note: 'naccept' declared here
int     accept(int, struct sockaddr *__restrict__, socklen_t *__restrict__);
        ^
/usr/include/sys/socket.h:168:25: note: expanded from macro 'accept'
#define accept          naccept
                        ^
sys_socket/accept4.c:46:27: error: use of undeclared identifier 'SOCK_CLOEXEC'
                                 SOCK_CLOEXEC);
                                 ^
2 errors generated.