clang -O2  -Wall -Wextra -Werror=implicit-function-declaration unistd/_Fork.c -o unistd/_Fork -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
unistd/_Fork.c:9:14: error: implicit declaration of function '_Fork' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        pid_t pid = _Fork();
                    ^
1 error generated.