check/delete-old: Auto-generate lib32 entries for libraries.

• Add usr/lib32/libfoo.so.N for lib/libfoo.so.N.

• Add usr/lib32/foo for usr/lib/foo.

• Treat casper libraries special since they are installed to /usr/lib32 instead of /usr/lib32/casper and thus map usr/lib/casper/foo to usr/lib32/foo.

Note that OLD_DIRS and MOVED_LIBS entries are not duplicated, only
OLD_FILES and OLD_LIBS.

Reviewed by: imp, emaste
Sponsored by: The University of Cambridge, Google Inc.
Differential Revision: https://reviews.freebsd.org/D33324