OpenBSD UBsan support procmaps

Summary: procmaps OpenBSD specifics

Patch by David CARLIER

Reviewers: krytarowski, vitalybuka

Reviewed By: vitalybuka

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

Differential Revision: https://reviews.llvm.org/D44050

llvm-svn: 327677