DUNE_PYTHON_EXTERNAL_VIRTUALENV_FOR_ABSOLUTE_BUILDDIR

Before Dune 2.7, the virtualenv was always placed inside the build directory of the first non-installed Dune module that the current module depends on. When using installed core modules or a multi-stage installation process, this can lead to situations where there are multiple virtualenvs, making it impossible to find all Python modules installed by upstream modules. In order to avoid this problem at least for builds using an absolute build directory (i.e., the --builddir option of dunecontrol refers to an absolute path), the build system will place the virtualenv in a dedicated directory dune-python-env inside that absolute build directory, where it will be found by all Dune modules. If you want to disable this behavior, set DUNE_PYTHON_EXTERNAL_VIRTUALENV_FOR_ABSOLUTE_BUILDDIR=0.