[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/ObjectFile/PECOFF/ObjectFilePECOFF.cpp

@@ -100,13 +100,13 @@ public:
   }
 };
 
+} // namespace
+
 static PluginProperties &GetGlobalPluginProperties() {
   static PluginProperties g_settings;
   return g_settings;
 }
 
-} // namespace
-
 static bool GetDebugLinkContents(const llvm::object::COFFObjectFile &coff_obj,
                                  std::string &gnu_debuglink_file,
                                  uint32_t &gnu_debuglink_crc) {