cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration strings/ffsll.c -o strings/ffsll -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
strings/ffsll.c:11:15: error: call to undeclared function 'ffsll'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
   11 |         int output = ffsll(input);
      |                      ^
1 error generated.