ProjectExplorer: Modernize

* Use override where appropriate
* Use pragma once
* Make more constructors explicit

Change-Id: I2865fe10f288e3de570826058e43b70a0cb4ee37
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/projectexplorer/clangparser.h

@@ -23,8 +23,7 @@
 **
 ****************************************************************************/
 
-#ifndef CLANGPARSER_H
-#define CLANGPARSER_H
+#pragma once
 
 #include "gccparser.h"
 #include "task.h"
@@ -51,5 +50,3 @@ private:
 };
 
 } // namespace ProjectExplorer
-
-#endif // CLANGPARSER_H