Quiet kotlin warnings

Avoid kotlin compiler printing warnings about debug test cases.

Bug: 65041640
Change-Id: Id1ad6f26a6f19ec959fe524e4ec998afafc78a92
diff --git a/build.gradle b/build.gradle
index 63513ce..7362238 100644
--- a/build.gradle
+++ b/build.gradle
@@ -565,6 +565,7 @@
             executable file("third_party/kotlin/kotlinc/bin/kotlinc");
         }
         args "-include-runtime"
+        args "-nowarn"
         args "-d"
         args "build/test/${kotlinHostJar}"
         args fileTree(dir: kotlinResourcesDir, include: '**/*.kt')