CppEditor: Add missing include

Change-Id: I559e07115eabf9c8bd22543422e59dbd3a574d06
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/cppeditor/cppindexingsupport.cpp

@@ -20,6 +20,7 @@
 #include <utils/temporarydirectory.h>
 
 #include <QLoggingCategory>
+#include <QRegularExpression>
 
 using namespace Utils;