Add NetBSD support in sanitizer_unwind_linux_libcdep.cc
NetBSD is a POSIX-like and BSD-family system.
Reuse FreeBSD and Linux code.
NetBSD uses DWARF ExceptionHandler.
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, kcc, filcab, vitalybuka
Reviewed By: vitalybuka
Subscribers: srhines, emaste, llvm-commits, kubamracek, aprantl, #sanitizers
Differential Revision: https://reviews.llvm.org/D36314