clang -O2  -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  -lintl
sys_socket/accept4.c:45:18: error: implicit declaration of function 'accept4' is invalid in C99 [-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 'accept'?
/usr/include/sys/socket.h:636:5: note: 'accept' declared here
int     accept(int, struct sockaddr * __restrict, socklen_t * __restrict);
        ^
1 error generated.