Synchronize PlatformNetBSD with Linux

Summary:
Update the code to the new world code.

These changes are needed for remote process plugin.

Sponsored by <The NetBSD Foundation>

Reviewers: emaste, clayborg, joerg, labath

Reviewed By: clayborg, labath

Subscribers: #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D29266

llvm-svn: 294145