ports-mgmt/portlint: Update to 2.19.12

In a discussion with members of the port managers team (tcberner, rene) the issue of conflicting package base names came up.

I have offered to create portlint checks for 2 possible Makefile issues:

1. Conflicting use of ${PKGBASE} of an existing port.

2. Multiple flavors resulting in the same ${PKGBASE}.

The attached patch adds checks for both possible issues:

1. Check for the existence of the new PKGBASE in the INDEX file (if present) and warn if it is used for a different ORIGIN.

2. Generate PKGBASE for all FLAVORS and check for duplicates.

PR: 263807