The mode_t type is defined in fcntl.h

--- a/snapper/FileUtils.h	2015-02-18 18:54:03.000000000 +0100
+++ b/snapper/FileUtils.h	2015-08-30 10:45:43.285166420 +0200
@@ -24,6 +24,7 @@
 #define SNAPPER_FILE_UTILS_H
 
 
+#include <fcntl.h>
 #include <string>
 #include <vector>
 #include <functional>