Also fixes the non-hybrid ARM assembler to display the instruction it
can't translate, making it easier to see what can't be handled. This
change was added to see what still isn't being translated in spec2k
performance tests.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4334
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1647113003 .