[XRay][clang] Allow clang to build XRay instrumented binaries in OpenBSD

[XRay][clang] Allow clang to build XRay instrumented binaries in OpenBSD

Summary:
This patch was originally reviewed in D45126. It enables clang to add
the XRay runtime and the link-time dependencies for XRay instrumentation
in OpenBSD.

Landing for devnexen.

Reviewers: brad, dberris

Subscribers: dberris, krytarowski, cfe-commits

Author: devnexen

Differential Revision: https://reviews.llvm.org/D45126

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@329183 91177308-0d34-0410-b5e6-96231b3b80d8