FallbackDir: orports: Introduce and use VecBuilder
This is part of #447 (closed) and therefore #371 (closed) and #285 (closed)
Found with
git-ls-files | xargs perl -ne 'next unless m/^\#.*derive.*Builder/..m/^\}/; print "$ARGV:$.:$_"' 2>&1 |less +/':.*Vec'
Edited by Ian Jackson