[PATCH] build-many-glibcs.py: Use --depth 1 in Git checkout

[Florian Weimer]

* Andreas Schwab:

> On Feb 28 2020, Florian Weimer wrote:
>
>> It really reduces checkout time, particularly if sourceware.org is under
>> load.
>
> Why can't you just use a local mirror?

I was trying to push builds out to a cluster of machines, and I don't
know where local is for each machine.

Thanks,
Florian