cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations sys_mman/O_RDWR.c -o sys_mman/O_RDWR -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
sys_mman/O_RDWR.c:3:17: error: use of undeclared identifier 'O_RDWR'
int const foo = O_RDWR;
                ^
1 error generated.