clang -O2  -Wall -Wextra -Werror=implicit-function-declaration strings/ffsl.c -o strings/ffsl -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
strings/ffsl.c:11:15: error: implicit declaration of function 'ffsl' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        int output = ffsl(input);
                     ^
strings/ffsl.c:11:15: note: did you mean 'ffs'?
/usr/include/strings.h:55:6: note: 'ffs' declared here
int      ffs(int);
         ^
1 error generated.