The santizer target is empty if no sanitizers are defined, otherwise
it contains the necessary targets. Because of this we can always
depend on it. Without this dep asan builds fail.

R=brettw@chromium.org, danno@chromium.org

Review URL: https://codereview.chromium.org/697763002

Patch from Scott Violet <sky@chromium.org>.

Cr-Commit-Position: refs/heads/master@{#25094}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25094 ce2b1a6d-e550-0410-aec6-3dcde31c8c00