veyron/tools/build: Print more detailed error information

Change-Id: I3f45edc21fbbc67330ccfd79b9dc09ccb7a68c43
diff --git a/tools/build/impl/impl.go b/tools/build/impl/impl.go
index 9804101..473ba65 100644
--- a/tools/build/impl/impl.go
+++ b/tools/build/impl/impl.go
@@ -219,11 +219,8 @@
 			}
 		}
 	}
-	for _, err := range errors {
-		fmt.Fprintf(command.Stderr(), "%v", err)
-	}
 	if len(errors) != 0 {
-		return fmt.Errorf("build failed")
+		return fmt.Errorf("build failed(%v)", errors)
 	}
 	return nil
 }