cc -O2 -pipe -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations unistd/_SC_XOPEN_UUCP.c -o unistd/_SC_XOPEN_UUCP -D_POSIX_C_SOURCE=202405L  -lm -lpthread -lrt  -lstdthreads -lcrypt
unistd/_SC_XOPEN_UUCP.c:2:17: error: use of undeclared identifier '_SC_XOPEN_UUCP'
    2 | int const foo = _SC_XOPEN_UUCP;
      |                 ^
1 error generated.