OpenBSD UBsan support missing bits

Summary:
Lost bits since the WIP ticket

Patch by David CARLIER

Reviewers: vitalybuka, vsk

Reviewed By: vitalybuka

Subscribers: srhines, kubamracek, krytarowski, fedor.sergeev, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D44599

llvm-svn: 327923