Fix fstream's assumptions about values of O_RDONLY, O_WRONLY, and O_RDWR.
Fix fstream's assumptions about values of O_RDONLY, O_WRONLY, and O_RDWR.

NoSuchProcess/ustl,msharov/ustl,dgruss/ustl,dgruss/ustl,msharov/ustl,Gerii/ustl,uusirant/ustl-cmake,uusirant/ustl-cmake,NoSuchProcess/ustl,Gerii/ustl