This project uses git submodules. To clone, run:

git clone --recursive git://git.build2.org/build2.git

Or:

git clone --recursive https://git.build2.org/build2.git

Alternatively, if you have already cloned without --recursive, run:

git submodule update --init

The checked out libbuild2/version.hxx and libbuild2/config.hxx will be
overwritten during the build process but these changes should be ignored. To
do this automatically, run:

git update-index --assume-unchanged libbuild2/version.hxx libbuild2/config.hxx