This is causing package build issues on OpenBSD because of a
difference in make behavior.
In GNU make, it always invoke the 'version.h' target, but then checks
to see if version.h changed before retriggering targets with that
prerequisite. On OpenBSD, invoking the version.h target always
retriggers targets with that prerequisite.
This means that updating the version information now requires a 'make
clean' or manual removal of version.h.