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/pp-scanner.h

@@ -43,8 +43,7 @@
   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
-#ifndef CPLUSPLUS_PP_SCANNER_H
-#define CPLUSPLUS_PP_SCANNER_H
+#pragma once
 
 namespace CPlusPlus {
 
@@ -118,5 +117,3 @@ struct pp_skip_argument
 };
 
 } // namespace CPlusPlus
-
-#endif // CPLUSPLUS_PP_SCANNER_H