We document this on our wiki and we might as well catch it in our CI
rather than waiting for it to be picked up on merge:

  https://wiki.qemu.org/Testing#clang_UBSan



Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>