[lldb] Place PlatformQemu Properties into anonymous namespace

It's fine right now, but will break as soon as someone else declares a
PluginProperties class in the same way.

Also tighten up the scope of the anonymous namespaces surrounding the
other PluginProperties classes.

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

@@ -166,13 +166,13 @@ public:
   }
 };
 
+} // namespace
+
 static PluginProperties &GetGlobalPluginProperties() {
   static PluginProperties g_settings;
   return g_settings;
 }
 
-} // namespace
-
 // TODO Randomly assigning a port is unsafe.  We should get an unused
 // ephemeral port from the kernel and make sure we reserve it before passing it
 // to debugserver.