First, check if the env program exists. If it does, it is faster than doing it via a python script `basically-env.py` that maybe imports all of mesonbuild.* as a side effect of project structure. We do not, however, use env for setting up PATH additions, since env can override an environment variable but not extend it. So in that case we still need to wrap the command via python. By default, all run_targets (at least) are wrapped and now wrap via the `env` program as they export e.g. MESONINTROSPECT='/usr/bin/meson introspect'