[libfuzzer] Add 'vptr' flag to builds with UndefinedBehaviourSanitizer.

security_blacklist.txt is a merge of blacklist.txt and vptr_blacklist.txt.

BUG=609786

Review-Url: https://codereview.chromium.org/2018973002
Cr-Commit-Position: refs/heads/master@{#397090}
5 files changed