clang -O2 -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations unistd/_POSIX_PRIO_IO.c -o unistd/_POSIX_PRIO_IO -D_POSIX_C_SOURCE=202405L -lm -lintl unistd/_POSIX_PRIO_IO.c:4:2: error: "_POSIX_PRIO_IO is not defined" #error "_POSIX_PRIO_IO is not defined" ^ 1 error generated.