Looking at the history of the original file in NetBSD, it is possible to
merge the copyright assignment that was made to The NetBSD Foundation.
This doesn't change anything as the license is still under 4-clause BSD
license but at a later time the NetBSD Foundation dropped Clauses 3 and 4
so this would help follow that change in the future.
This is, of course, taken from NetBSD CVS:
Although there is an intermediate change that doesn't apply to us (CVS 1.12).
FWIW, I also looked at sysv_shm.c, but relicensing that would be much more
complex as they rewrote most of the code.