clang -O2  -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  -lintl
sys_mman/O_EXCL.c:3:17: error: use of undeclared identifier 'O_EXCL'
int const foo = O_EXCL;
                ^
1 error generated.