Specifically, it moves

lowerArguments
lowerRet
addProlog
addEpilog

from the x86 lowering template to the concrete lowering implementations.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4077
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1261383002.