Instead of explicitly add the target associated to the toolchain
if we use `build_nodeps` option let add an attribute base ourself on it
to know if we need to add it or not.
This way, we may have other dependency we must not skip.
Instead of having the run_command function setting the
env from the buildEnv, this is the dependency that create the
env and then pass it to the run_command function.
This way, each dependency will be able to set a specific env.
Matthieu Gautier