This variable should be pure MI except possibly for reading it in MD
dump routines. Its initialization was pure MD in 4.4BSD, but FreeBSD
changed this in r36441 in 1998. There were many imperfections in
r36441. This commit fixes only a small one, to simplify fixing the
others 1 arch at a time. (r47678 added support for
special/early/multiple message buffer initialization which I want in
a more general form, but this was too fragile to use because hacking
on the msgbufp global corrupted it, and was only used for 5 hours in
-current...)
d81660feeb