Pin submodule utfcpp to tag v4.0.9 (#1315)

git submodule init
git submodule update --remote
(cd 3rdparty/utfcpp && git checkout v4.0.9)
git add 3rdparty/utfcpp
git commit -m 'Pin submodule utfcpp to tag v4.0.9'

Author: ufleisch