This CL implements two little pieces of the lowering that are needed
for --filetype=obj support in arm. With this change, spec2k builds and
verifies with --filetype=obj

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

Review URL: https://codereview.chromium.org/1651603003 .