Squashed 'third-party/bashflags/' content from commit fc44bda

git-subtree-dir: third-party/bashflags
git-subtree-split: fc44bda1bcf19ceba1342ab5755dbb339fde9dd5
import 'bashflags' from github/bholt/bashflags.git at third-party/bashflags
use bashflags rather than what was in common.sh
copy bashflags into build dir