Move detach to FreeBSD- and Linux-specific classes.

On Linux there is no separate notion of a process (vs. a thread) for
ptrace(); each thread needs to be individually detached.  On FreeBSD
we have a separate process context, and we detach just it.

Review: http://llvm-reviews.chandlerc.com/D1418
llvm-svn: 189666
diff --git a/lldb/source/Plugins/Process/Linux/ProcessLinux.h b/lldb/source/Plugins/Process/Linux/ProcessLinux.h
index 742627f..15193b8 100644
--- a/lldb/source/Plugins/Process/Linux/ProcessLinux.h
+++ b/lldb/source/Plugins/Process/Linux/ProcessLinux.h
@@ -54,6 +54,9 @@
                  lldb_private::Listener &listener,
                  lldb_private::FileSpec *core_file);
 
+    virtual lldb_private::Error
+    DoDetach(bool keep_stopped);
+
     virtual bool
     UpdateThreadList(lldb_private::ThreadList &old_thread_list, lldb_private::ThreadList &new_thread_list);