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/cplusplus/PreprocessorClient.h

@@ -23,8 +23,7 @@
 **
 ****************************************************************************/
 
-#ifndef PREPROCESSORCLIENT_H
-#define PREPROCESSORCLIENT_H
+#pragma once
 
 #include <cplusplus/CPlusPlusForwardDeclarations.h>
 
@@ -118,5 +117,3 @@ public:
 };
 
 } // namespace CPlusPlus
-
-#endif // PREPROCESSORCLIENT_H