* Don't require 16-byte CAS on x86.
We only need to CAS 2 pointers, which is always possible on x86.
* Fix the way the Image variable is referenced.
* Replace failOnStderr by `set -eo pipefail` on Linux.
The x86 image doesn't have clangformat, which causes cmake to print a
warning on the stderr. Exit codes should be enough to detect failure.
* Use x86 images from snmallocciteam.
* clang-format
