Reuse appropriate Launch and Attach on NetBSD

Summary:
NetBSD ships with NativeProcessNetBSD  inherited from NativeProcessProtocol.

Link Plugins/Process/gdb-remote with lldbPluginProcessNetBSD in order to resolve
correctly the linking to Launch and Attach from the NetBSD plugin.

Sponsored by <The NetBSD Foundation>

Reviewers: kettenis, labath, emaste, joerg

Reviewed By: labath, emaste

Subscribers: mgorny, #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D31231

llvm-svn: 298524