[fixes issue #1759] We removed the ‘flag usage’ check on builder instead of replacing it with the non-experimental check about 3 years ago when builder moved out of experimental. The check has now been restored.

src/core/lombok/javac/handlers/HandleBuilder.java

@@ -99,6 +99,8 @@ public class HandleBuilder extends JavacAnnotationHandler<Builder> {
 	}
 	
 	@Override public void handle(AnnotationValues<Builder> annotation, JCAnnotation ast, JavacNode annotationNode) {
+		handleFlagUsage(annotationNode, ConfigurationKeys.BUILDER_FLAG_USAGE, "@Builder");
+		
 		Builder builderInstance = annotation.getInstance();
 		
 		// These exist just to support the 'old' lombok.experimental.Builder, which had these properties. lombok.Builder no longer has them.