clang -O2  -Wall -Wextra -Werror=implicit-function-declaration stdlib/getsubopt.c -o stdlib/getsubopt -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
stdlib/getsubopt.c:21:15: error: implicit declaration of function 'getsubopt' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        int result = getsubopt(&options, keys, &value);
                     ^
1 error generated.