libziparchive: fix mac os breakage

Add ftruncate64 to utils/Compat.h definitions for mac.

Change-Id: I82cb46927be911e867b606f4f4429a5e1b1987f7
Test: builds on mac
diff --git a/libziparchive/zip_writer.cc b/libziparchive/zip_writer.cc
index ddd4dd5..7600528 100644
--- a/libziparchive/zip_writer.cc
+++ b/libziparchive/zip_writer.cc
@@ -25,6 +25,7 @@
 #include <vector>
 
 #include "android-base/logging.h"
+#include "utils/Compat.h"
 #include "utils/Log.h"
 
 #include "entry_name_utils-inl.h"