Wholesale conversion to #pragma once

Kudos to cgmb and https://github.com/cgmb/guardonce

Change-Id: Ifa8970734b8d43fd08c9260c645bdb0228633791
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/libs/qmljs/parser/qmljskeywords_p.h

@@ -23,8 +23,7 @@
 **
 ****************************************************************************/
 
-#ifndef QMLJSKEYWORDS_P_H
-#define QMLJSKEYWORDS_P_H
+#pragma once
 
 //
 //  W A R N I N G
@@ -875,5 +874,3 @@ int Lexer::classify(const QChar *s, int n, bool qmlMode) {
 } // namespace QmlJS
 
 QT_QML_END_NAMESPACE
-
-#endif // QMLJSKEYWORDS_P_H