util-docker,tests: Add GCC-12 compiler image and test

This increases gem5's supported compiler up to GCC Version 12

Change-Id: Ifed5b8456bd1ab36a2fa58d8be7911acbef29bdd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/64174
Reviewed-by: Kunal Pai <kunpai@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
3 files changed