Log Message:
Fix build of db{4,46,5} on MirBSD.

The build does not create all those unnecessary shlib symlinks on MirBSD
(I believe this is due to a patch I sent in years ago), so add separate
PLIST.MirBSD files that do not contain these files.

(BTW, I would be grateful to learn how I can achieve the same effect
without copying PLISTs, but this works.)