implement the null function for the Mips32 subzero compiler

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4167
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/1176133004 .

Patch from Reed Kotler <reed.kotler@imgtec.com>.
9 files changed