Initial dependency file generation

src/build_settings.cpp

@@ -831,6 +831,7 @@ struct BuildContext {
 	bool   show_timings;
 	TimingsExportFormat export_timings_format;
 	String export_timings_file;
+	String export_dependencies_file;
 	bool   show_unused;
 	bool   show_unused_with_location;
 	bool   show_more_timings;