configs: Python 3.2+ requires additional flag for makedirs

makedirs requires and additional flag for makedirs to ignore
error when the directory exists. This change enables overwriting
on existing output directories for a simulation.
https://docs.python.org/3/library/os.html

Change-Id: I1c7329ded1f5eef2c882e3224457e1d991d074fd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58190
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed