Replace pragma once with header guards for consistency

Only 2 headers have this.

src/core/iconmapper.h

@@ -17,7 +17,8 @@
  *
  */
 
-#pragma once
+#ifndef ICONMAPPER_H
+#define ICONMAPPER_H
 
 #include "config.h"
 
@@ -135,3 +136,6 @@ static const QMap<QString, IconProperties> iconmapper_ = {  // clazy:exclude=non
 };
 
 }  // namespace IconMapper
+
+#endif  // ICONMAPPER_H
+

src/core/stylehelper.h

@@ -23,7 +23,6 @@
 **
 ****************************************************************************/
 
-//#pragma once
 #ifndef STYLEHELPER_H
 #define STYLEHELPER_H
 

src/core/translations.h

@@ -17,7 +17,8 @@
  *
  */
 
-#pragma once
+#ifndef TRANSLATIONS_H
+#define TRANSLATIONS_H
 
 #include "config.h"
 
@@ -39,3 +40,5 @@ class Translations : public QObject {
   QList<QTranslator*> translations_;
 
 };
+
+#endif  // TRANSLATIONS_H