Add NetBSD case in Entry::Type::ThreadID

Summary:
NetBSD native threads are printed as 64-bit unsigned integers.

The underlying system type of a thread identity is lwpid_t of type int32_t. For consistency with Linux and FreeBSD share the 64-bit unsigned integer type.

Sponsored by <The NetBSD Foundation>

Reviewers: labath, kettenis, joerg, emaste

Reviewed By: labath, emaste

Subscribers: #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D31132

llvm-svn: 298405