OpenBSD Driver basic sanitiser support

Summary:
Basic support of Sanitiser to follow-up ubsan support in compiler-rt.
Needs to use lld instead of base ld to be fully workable.

Patch by: David CARLIER

Reviewers: krytarowski, vitalybuka, kettenis

Reviewed By: vitalybuka

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D43961

llvm-svn: 326648