Merged r15601 into trunk branch.

MIPS: Replace custom builtin invocation instructions by a generic version.

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/18502003

git-svn-id: https://v8.googlecode.com/svn/trunk@15614 ce2b1a6d-e550-0410-aec6-3dcde31c8c00