Clang: Improve interfaces

The interfaces should never used to handle ownership. So it is now using
protected destructors. Copy operations are forbidden too.

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c35-a-base-class-destructor-should-be-either-public-and-virtual-or-protected-and-nonvirtual

Change-Id: Ib0b60a73a7ec130973b5cb0095cc5b2f10fa0758
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/libs/clangsupport/connectionclient.h

@@ -54,7 +54,9 @@ class CLANGSUPPORT_EXPORT ConnectionClient : public QObject
 
 public:
     ConnectionClient(const QString &connectionName);
-    virtual ~ConnectionClient();
+
+    ConnectionClient(const ConnectionClient &) = delete;
+    ConnectionClient &operator=(const ConnectionClient &) = delete;
 
     void startProcessAndConnectToServerAsynchronously();
     void disconnectFromServer();
@@ -82,6 +84,9 @@ signals:
     void disconnectedFromLocalSocket();
     void processFinished();
 
+protected:
+    ~ConnectionClient();
+
 protected:
     QIODevice *ioDevice();
     const QTemporaryDir &temporaryDirectory() const;