Reapply r332965 (by emaste):

lldb: remove assertion that target_arch is FreeBSD

The target is not necessarily a FreeBSD binary - for example, it may be
a Linux binary running under the linuxulator. Basic ptrace (live)
debugging already worked in this case, except for the assertion.

Sponsored by: Turing Robotic Industries Inc.

(cherry picked from commit 165786983df7513a6ab99dfe42e9526e46816ca5)