NetBSD ships with POSIX strerror_r(3)

Summary:
Switch NetBSD from GNU to the POSIX strerror_r(3) interceptor.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, eugenis, vitalybuka

Reviewed By: vitalybuka

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

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D41019

llvm-svn: 320221