'From the pointer *clo* to a _dynfunc.Closure, get a pointer
to the enclosed _dynfunc.Environment.'

def get_env_from_closure(self, builder, clo):

    with cgutils.if_unlikely(builder, cgutils.is_null(builder, clo)):
        self.debug_print(builder, 'Fatal    error:    missing    _dynfunc.Closure')
        builder.unreachable()
    clo_body_ptr = cgutils.pointer_add(builder, clo, _dynfunc._impl_info['offsetof_closure_body'])
    clo_body = ClosureBody(self, builder, ref=clo_body_ptr, cast_ref=True)
    return clo_body.env
