Handle stack spills in ARM integrated assembler.

Add code to handle spilling stack variables. That is, add code to
handle loading and storing to stack addresses.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4334
R=jpp@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1402403002 .
6 files changed