gcc -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations sys_mman/O_EXCL.c -o sys_mman/O_EXCL -D_POSIX_C_SOURCE=202405L -lm -lpthread -lrt -lxnet -lsocket -latomic
sys_mman/O_EXCL.c:3:17: error: 'O_EXCL' undeclared here (not in a function)
    3 | int const foo = O_EXCL;
      |                 ^~~~~~