Otherwise there are constant warnings

Change-Id: I5409a2871950413a12140f0550b2d45bfea9abc5
Reviewed-on: https://fuchsia-review.googlesource.com/c/fargo/+/592764
Reviewed-by: Marc Khouri <mnck@google.com>
diff --git a/src/lib.rs b/src/lib.rs
index 1eaef45..5761ac0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -403,6 +403,7 @@
     let mut rust_flags = vec![
         "-L".to_string(),
         sysroot_lib.to_string(),
+        "-Aunknown-lints".to_string(),
         "-Cpanic=abort".to_string(),
         "-Zpanic_abort_tests".to_string(),
         // Add an extra config to let crates like scoped_task know we're compiling with