Fix GN build.

Bug b/115344057
Bug chromium:881334

Change-Id: Ib54e43a106c17b4878780382c4a80415e8f3583b
Reviewed-on: https://swiftshader-review.googlesource.com/c/21508
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/.gitignore b/.gitignore
index 646457b..61a991c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 /lib/
 /obj/
 /bin/
+/out/
 /build/
 .vs