clang -O2  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations unistd/fdatasync.c -o unistd/fdatasync -D_POSIX_C_SOURCE=202405L  -lm  -lintl
unistd/fdatasync.c:6:19: error: use of undeclared identifier 'fdatasync'
int (*foo)(int) = fdatasync;
                  ^
1 error generated.