/opt/IBM/openxlC/17.1.1/bin/ibm-clang -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 -latomic
sys_mman/O_EXCL.c:3:17: error: use of undeclared identifier 'O_EXCL'
int const foo = O_EXCL;
                ^
1 error generated.