cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations fcntl/POSIX_FADV_WILLNEED.c -o fcntl/POSIX_FADV_WILLNEED -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
fcntl/POSIX_FADV_WILLNEED.c:3:17: error: use of undeclared identifier 'POSIX_FADV_WILLNEED'
int const foo = POSIX_FADV_WILLNEED;
                ^
1 error generated.