Auto-build/update codegen

Test: 1. Manually enter version/presence of build artifact,
and ensure `codegen FILENAME` still works
2. run codegen again without altering version, ensure no build triggered
Change-Id: I6f1dba0a476077c708bbea8ef558445107e5ad97
diff --git a/tools/codegen/Android.bp b/tools/codegen/Android.bp
index 805b296..677bee2 100644
--- a/tools/codegen/Android.bp
+++ b/tools/codegen/Android.bp
@@ -1,5 +1,5 @@
 java_binary_host {
-    name: "codegen",
+    name: "codegen_cli",
     manifest: "manifest.txt",
     srcs: [
         "src/**/*.kt",