OpenBSD UBsan support / common

Summary:
Sanitizer common, enable OpenBSD platform.
- Enable common interceptors as possible and create few distinct ones.
- Create necessary sanitizer_struct types.

Patch by: David CARLIER

Reviewers: krytarowski, vitalybuka, visa, kettenis

Reviewed By: vitalybuka

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

Differential Revision: https://reviews.llvm.org/D43909

llvm-svn: 326650