[C++] Fix exec.cc, so it checks timestamps properly
diff --git a/fileutil.h b/fileutil.h
index eee2f09..22355f8 100644
--- a/fileutil.h
+++ b/fileutil.h
@@ -18,5 +18,6 @@
 #include "string_piece.h"
 
 bool Exists(StringPiece f);
+double GetTimestamp(StringPiece f);
 
 #endif  // FILEUTIL_H_