Use -O2 instead -O3 for Android build.

It produces smaller binary with almost the same performance.

R=benm@chromium.org, jkummerow@chromium.org

Review URL: https://chromiumcodereview.appspot.com/15929009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15071 ce2b1a6d-e550-0410-aec6-3dcde31c8c00