/opt/IBM/openxlC/17.1.1/bin/ibm-clang -pthread  -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 -lpthread -lrt -latomic
unistd/_Fork.c:9:14: error: call to undeclared function '_Fork'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        pid_t pid = _Fork();
                    ^
1 error generated.