Move to Weld as the build system.

Change-Id: I7c9704f3f310cf7e5410db148a9c4c589914b0f2
diff --git a/.gitignore b/.gitignore
index 1bbd63d..7a17acd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,4 @@
-hello-world-ng
-t/greeting-test
 *~
 *.o
-/test-results
\ No newline at end of file
+/test-results
+/build