Log Message:
elasticsearch: Update to 6.8.8.

I'm unable to find a useful changelog, so unfortunately if you want to see
what has changed since 6.4.0 then you'll need to head over to
https://www.elastic.co/guide/en/elasticsearch/reference/6.8/es-release-notes.html
and read each of the individual links for every single point release.

While here fix some build issues and pkglint warnings.