The compiler tests are failing to to a compile bug in Clang 7: https://github.com/gem5/gem5/actions/runs/10170081794 Given Ubuntu 20.04 APT installs v10 by default (i.e., with `apt install clang`). This is the oldest LTS Ubuntu version. It therefore seems sensible to drop support for older (<v10) versions of clang. Change-Id: I4c48223b80306422beac1464c09f03397c156ba1