Finalize ASAN/NetBSD

Summary:
This revision contains various cleanups.

Sponsored by <The NetBSD Foundation>

Reviewers: kcc, vitalybuka, joerg, eugenis

Reviewed By: kcc

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

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D37244

llvm-svn: 312188