cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration unistd/encrypt.c -o unistd/encrypt -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
unistd/encrypt.c:15:2: error: call to undeclared function 'setkey'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        setkey(key);
        ^
unistd/encrypt.c:19:2: error: call to undeclared function 'encrypt'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        encrypt(buffer, 0);
        ^
unistd/encrypt.c:19:2: note: did you mean 'crypt'?
/usr/include/unistd.h:408:7: note: 'crypt' declared here
char    *crypt(const char *, const char *);
         ^
2 errors generated.