Enable COMPILER_RT_HAS_SANITIZER_COMMON on NetBSD

Summary:
Temporarily keep disabled COMPILER_RT_HAS_ASAN on NetBSD.

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, filcab, kcc, vitalybuka

Reviewed By: vitalybuka

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

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D36312

llvm-svn: 310370