Use C++11’s override and remove virtual where applicable

Fixes warning: prefer using 'override' or (rarely) 'final' instead of
'virtual' [modernize-use-override]

Change-Id: I4b8b8ecce028dfd051fe14984b40115e92057a40
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/synchronousprocess.cpp

@@ -90,7 +90,7 @@ public:
     void setFlags(unsigned tc) { m_flags = tc; }
 
 protected:
-    virtual void setupChildProcess();
+    void setupChildProcess() override;
 
 private:
     unsigned m_flags;