clang -O2  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations unistd/_XOPEN_REALTIME.c -o unistd/_XOPEN_REALTIME -D_POSIX_C_SOURCE=202405L  -lm  -lintl
unistd/_XOPEN_REALTIME.c:9:2: error: "_XOPEN_REALTIME is not defined"
#error "_XOPEN_REALTIME is not defined"
 ^
1 error generated.