util-docker,tests: Add Clang-13 compiler image and test

This increases gem5's supported compiler up to Clang Version 13.

Change-Id: I5a9b602b67626b195dcd8e297abbcfb70cf83cbe
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/64175
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
3 files changed