cc -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations sys_socket/SO_PROTOCOL.c -o sys_socket/SO_PROTOCOL -D_POSIX_C_SOURCE=202405L  -lm -lpthread  -liconv
sys_socket/SO_PROTOCOL.c:2:17: error: use of undeclared identifier 'SO_PROTOCOL'
    2 | int const foo = SO_PROTOCOL;
      |                 ^
1 error generated.