[lldb] Fix "code requires global destructor" warning in g_architecture_mutex

[kubamracek]

Ping.

[davide]

LGTM.

lldb/trunk/source/Core/PluginManager.cpp

 struct ArchitectureInstance {
   ConstString name;
   std::string description;
   PluginManager::ArchitectureCreateInstance create_callback;
 };
 
 typedef std::vector<ArchitectureInstance> ArchitectureInstances;
 
+static std::mutex &GetArchitectureMutex() {
     static std::mutex g_architecture_mutex;
+    return g_architecture_mutex;
+}
 
 static ArchitectureInstances &GetArchitectureInstances() {
   static ArchitectureInstances g_instances;
   return g_instances;
 }
 
 void PluginManager::RegisterPlugin(const ConstString &name,
                                    llvm::StringRef description,
                                    ArchitectureCreateInstance create_callback) {
-  std::lock_guard<std::mutex> guard(g_architecture_mutex);
+  std::lock_guard<std::mutex> guard(GetArchitectureMutex());
   GetArchitectureInstances().push_back({name, description, create_callback});
 }
 
 void PluginManager::UnregisterPlugin(
     ArchitectureCreateInstance create_callback) {
-  std::lock_guard<std::mutex> guard(g_architecture_mutex);
+  std::lock_guard<std::mutex> guard(GetArchitectureMutex());
   auto &instances = GetArchitectureInstances();
 
   for (auto pos = instances.begin(), end = instances.end(); pos != end; ++pos) {
     if (pos->create_callback == create_callback) {
       instances.erase(pos);
       return;
     }
   }
   llvm_unreachable("Plugin not found");
 }
 
 std::unique_ptr<Architecture>
 PluginManager::CreateArchitectureInstance(const ArchSpec &arch) {
-  std::lock_guard<std::mutex> guard(g_architecture_mutex);
+  std::lock_guard<std::mutex> guard(GetArchitectureMutex());
   for (const auto &instances : GetArchitectureInstances()) {
     if (auto plugin_up = instances.create_callback(arch))
       return plugin_up;
   }
   return nullptr;
 }
 
 #pragma mark Disassembler