Remove global symbols: Avoid using the global namespace if possible

Rename CCriticalSection to RecursiveMutex (both are AnnotatedMixin<std::recursive_mutex>)

```
$ git grep -E '(typedef|using).*(CCriticalSection|RecursiveMutex)'
src/sync.h:using RecursiveMutex = AnnotatedMixin<std::recursive_mutex>;
src/sync.h:typedef AnnotatedMixin<std::recursive_mutex> CCriticalSection;
```

src/httpserver.cpp

@@ -139,15 +139,15 @@ struct HTTPPathHandler
 //! libevent event loop
 static struct event_base* eventBase = nullptr;
 //! HTTP server
-struct evhttp* eventHTTP = nullptr;
+static struct evhttp* eventHTTP = nullptr;
 //! List of subnets to allow RPC connections from
 static std::vector<CSubNet> rpc_allow_subnets;
 //! Work queue for handling longer requests off the event loop thread
 static WorkQueue<HTTPClosure>* workQueue = nullptr;
 //! Handlers for (sub)paths
-std::vector<HTTPPathHandler> pathHandlers;
+static std::vector<HTTPPathHandler> pathHandlers;
 //! Bound listening sockets
-std::vector<evhttp_bound_socket *> boundSockets;
+static std::vector<evhttp_bound_socket *> boundSockets;
 
 /** Check if a network address is allowed to access the HTTP server */
 static bool ClientAllowed(const CNetAddr& netaddr)
@@ -420,7 +420,7 @@ bool UpdateHTTPServerLogging(bool enable) {
 #endif
 }
 
-std::thread threadHTTP;
+static std::thread threadHTTP;
 static std::vector<std::thread> g_thread_http_workers;
 
 void StartHTTPServer()

src/init.cpp

@@ -74,7 +74,7 @@
 #include <zmq/zmqrpc.h>
 #endif
 
-bool fFeeEstimatesInitialized = false;
+static bool fFeeEstimatesInitialized = false;
 static const bool DEFAULT_PROXYRANDOMIZE = true;
 static const bool DEFAULT_REST_ENABLE = false;
 static const bool DEFAULT_STOPAFTERBLOCKIMPORT = false;

src/warnings.cpp

@@ -8,10 +8,10 @@
 #include <util/system.h>
 #include <warnings.h>
 
-CCriticalSection cs_warnings;
+static RecursiveMutex cs_warnings;
-std::string strMiscWarning GUARDED_BY(cs_warnings);
+static std::string strMiscWarning GUARDED_BY(cs_warnings);
-bool fLargeWorkForkFound GUARDED_BY(cs_warnings) = false;
+static bool fLargeWorkForkFound GUARDED_BY(cs_warnings) = false;
-bool fLargeWorkInvalidChainFound GUARDED_BY(cs_warnings) = false;
+static bool fLargeWorkInvalidChainFound GUARDED_BY(cs_warnings) = false;
 
 void SetMiscWarning(const std::string& strWarning)
 {