Handle libarchive API change in archive_read_data_block

The offset argument type depends on the libarchive version.

Source/cmSystemTools.cxx

@@ -1866,7 +1866,11 @@ long copy_data(struct archive *ar, struct archive *aw)
   long r;
   const void *buff;
   size_t size;
+#if defined(ARCHIVE_VERSION_NUMBER) && ARCHIVE_VERSION_NUMBER >= 3000000
+  __LA_INT64_T offset;
+#else
   off_t offset;
+#endif
 
   for (;;)
     {