The buildconfig module predates MozbuildObject.from_environment, and
it's about time to start factoring things out such that we only have
one way to get config.status data. This is step 1: making the
buildconfig module use MozbuildObject.from_environment.
Eventually, we'll want to remove the buildconfig module uses everywhere.
So far, we relied on the module being copied over in the virtualenv, and
the module itself would try to find config.status in parent directories
of its own location. Unfortunately, this falls short when the source
tree's build/ directory appears early in the sys.path.
With this change, we don't copy the module to the virtualenv anymore,
and try to find config.status in parent directories of the python
executable, which, when running from the virtualenv, will be equivalent
to the current behavior.
