cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations strings/ffsll.c -o strings/ffsll -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
strings/ffsll.c:11:25: error: use of undeclared identifier 'ffsll'
int (*foo)(long long) = ffsll;
                        ^
1 error generated.