This makes the urandom codebase easier to maintain by allowing porting patches between 2.7 and 3.x easier; it also improves support for the OpenBSD platform.

Support for porting patches is not just a theoretical concern, it's likely that Linux's getrandom() will be supported at some point; like getentropy() it's useful because it's less error prone, and works in chroots and other environments that don't explicitly set up the /dev/urandom device.