data: Option to run only C/C++ preprocessor when indexing (issue 297)

* Added as checkbox to indexing start dialog
* Only shown for C/C++ projects
* Files will be marked incomplete

src/lib_gui/qt/element/QtHelpButton.h

@@ -0,0 +1,21 @@
+#ifndef QT_HELP_BUTTON_H
+#define QT_HELP_BUTTON_H
+
+#include "qt/element/QtIconButton.h"
+
+class QtHelpButton
+	: public QtIconButton
+{
+	Q_OBJECT
+
+public:
+	QtHelpButton(const QString& helpText, QWidget* parent = nullptr);
+
+private slots:
+	void handleHelpPress();
+
+private:
+	QString m_helpText;
+};
+
+#endif // QT_HELP_BUTTON_H