Use the nice macro to declare once-init control objects, like good little coders…

Use the nice macro to declare once-init control objects, like good little coders should.  Otherwise the initialization routines never run on Mac.  TODO:  Investigate how this was broken.

src/google/protobuf/descriptor.cc

@@ -798,7 +798,7 @@ namespace {
 
 EncodedDescriptorDatabase* generated_database_ = NULL;
 DescriptorPool* generated_pool_ = NULL;
-GoogleOnceType generated_pool_init_;
+GOOGLE_PROTOBUF_DECLARE_ONCE(generated_pool_init_);
 
 void DeleteGeneratedPool() {
   delete generated_database_;

src/google/protobuf/extension_set.cc

@@ -76,7 +76,7 @@ struct ExtensionInfo {
 typedef hash_map<pair<const MessageLite*, int>,
                  ExtensionInfo> ExtensionRegistry;
 ExtensionRegistry* registry_ = NULL;
-GoogleOnceType registry_init_;
+GOOGLE_PROTOBUF_DECLARE_ONCE(registry_init_);
 
 void DeleteRegistry() {
   delete registry_;