Log Message:
pkgtools/pkglint: update to 19.4.0

Changes since 19.3.19:

Empty PLIST files now generate an error instead of a warning since there
is no reason for having these empty files.

If a follow-up line in a Makefile is completely empty, there is no note
about trailing whitespace anymore since the warning about the misleading
empty line already covers this case.

The remaining code changes are only refactorings.