reftable: write reftable files

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Makefile b/Makefile
index 2e5a9f4..05be433 100644
--- a/Makefile
+++ b/Makefile
@@ -2463,6 +2463,7 @@
 REFTABLE_OBJS += reftable/publicbasics.o
 REFTABLE_OBJS += reftable/record.o
 REFTABLE_OBJS += reftable/tree.o
+REFTABLE_OBJS += reftable/writer.o
 
 REFTABLE_TEST_OBJS += reftable/basics_test.o
 REFTABLE_TEST_OBJS += reftable/block_test.o