Re: [PATCH 05/11] builtin/repack.c: avoid leaking child arguments

> `git repack` invokes a handful of child processes: one to write the
> actual pack, and optionally ones to repack promisor objects and update
> the MIDX.
>
> In none of these cases do we bother to call child_process_clear(), which
> frees the memory associated with each child's arguments and environment.
>
> In order to do so, tweak each function that spawns a child process to
> have a `cleanup` label that we always visit before returning from each
> function. Then, make sure that we call child_process_clear() as a part
> of that label.