Revert "simplify to just using INSTALLDIRS"

This reverts commit b973f26437a7d0584a73d6e1bf8c08a15873b82a.

If 1.17 was installed, it would be in archlib, so 1.18-1.19 would
fail to be located due to @INC ordering.  Reported by MIYAGAWA.
prep next release