hxcpp is the runtime support for the c++ backend of the haxe compiler. This contains the headers, libraries and support code required to generate a fully compiled executable from haxe code.
REPO=$(pwd)
cd ${REPO}/tools/run
haxe compile.hxml
cd ${REPO}/tools/hxcpp
haxe compile.hxml
cd $REPO
You first need to build the cppia host.
REPO=$(pwd)
cd ${REPO}/project
haxe compile-cppia.hxml
cd $REPO
Then you can do haxelib run hxcpp file.cppia.