Set up crosstest to run simple loop in Om1 on ARM.

We can't run O2 yet because some of the advanced Phi lowering
hooks aren't implemented for O2 yet.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4076
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1160873006.