Core: Use Qt5-style connects

The heavy lifting was done by clazy.

Change-Id: I2dde14919d917816d02117338205f8f861d8af0a
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/coreplugin/externaltool.h

@@ -129,14 +129,13 @@ public:
     bool hasError() const;
     QString errorString() const;
 
-private slots:
+private:
     void started();
     void finished(int exitCode, QProcess::ExitStatus status);
     void error(QProcess::ProcessError error);
     void readStandardOutput();
     void readStandardError();
 
-private:
     void run();
     bool resolve();