Cleanup: hide undefined behavior from the compiler better.

Submitting this on behalf of Paul Pluzhnikov.

R=mark@chromium.org

Review URL: https://breakpad.appspot.com/6674002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1342 4c0a9323-5329-0410-9bdc-e9ce6186880e