Make untar.c build correctly with libarchive 3.0.

SVN-Revision: 3719

examples/untar.c

@@ -200,7 +200,11 @@ copy_data(struct archive *ar, struct archive *aw)
 	int r;
 	const void *buff;
 	size_t size;
+#if ARCHIVE_VERSION >= 3000000
+	int64_t offset;
+#else
 	off_t offset;
+#endif
 
 	for (;;) {
 		r = archive_read_data_block(ar, &buff, &size, &offset);