robolectric requires autobuilder to build.

Test: atest . in /external/robolectric (failing)
Bug: 244627502
Change-Id: I0a5bc44fb0ef479f5a64528cc91c2c4ab997b084
diff --git a/value/Android.bp b/value/Android.bp
index 24e40a6..4d174d1 100644
--- a/value/Android.bp
+++ b/value/Android.bp
@@ -64,6 +64,13 @@
 }
 
 java_plugin {
+    name: "auto_value_builder_plugin",
+    static_libs: ["libauto_value_plugin"],
+    processor_class: "com.google.auto.value.processor.AutoBuilderProcessor",
+    visibility: ["//visibility:public"],
+}
+
+java_plugin {
     name: "auto_oneof_plugin",
     static_libs: [
         "libauto_value_plugin",