Enable ProcessPOSIXLog on NetBSD

Summary:
NetBSD can share the same logging functionality with Linux and FreeBSD.

Sponsored by <The NetBSD Foundation>


Reviewers: labath, emaste, joerg, kettenis

Reviewed By: labath, emaste

Subscribers: #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D31191

llvm-svn: 298406