MIPS: Add function declarations missing from r18000.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/83423002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18027 ce2b1a6d-e550-0410-aec6-3dcde31c8c00