Enable SANITIZER_INTERCEPTOR_HOOKS for NetBSD

Summary:
This feature is required for proper libFuzzer support.

Adding SI_NETBSD to the list of OSes, fixes breakage in several
libFuzzer tests. It has been debugged with aid from kcc@.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka, kcc

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D46729

llvm-svn: 332051