added b64.c to the sources neede for grpc_base
diff --git a/build.yaml b/build.yaml
index 7c43df3..d43e156 100644
--- a/build.yaml
+++ b/build.yaml
@@ -359,6 +359,7 @@
   - src/core/lib/json/json_reader.c
   - src/core/lib/json/json_string.c
   - src/core/lib/json/json_writer.c
+  - src/core/lib/security/util/b64.c
   - src/core/lib/slice/percent_encoding.c
   - src/core/lib/slice/slice.c
   - src/core/lib/slice/slice_buffer.c