Add NetBSD support in sanitizer_libignore.cc

Summary:
Reuse Linux, FreeBSD and Apple code - no NetBSD specific changes.

Part of the code inspired by the original work on libsanitizer in GCC 5.4 by Christos Zoulas.
    
Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka, filcab, kcc

Reviewed By: filcab

Subscribers: emaste, kubamracek, llvm-commits

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D35628

llvm-svn: 308616