Update test.dart for detection output of machine formatted errors

tests/language/src/Prefix23NegativeTest.dart

Index: tests/language/src/Prefix23NegativeTest.dart
diff --git a/tests/language/src/Prefix23NegativeTest.dart b/tests/language/src/Prefix23NegativeTest.dart
index 7819e900cc91acf63aa33e3a10380c1b8a7afc29..ec111e10953ceb2f99ebb0f7c3b26d90281d5313 100644
--- a/tests/language/src/Prefix23NegativeTest.dart
+++ b/tests/language/src/Prefix23NegativeTest.dart
@@ -4,13 +4,13 @@
 //
 // Unresolved symbols should be reported as an static type warnings.
 // In this variant of test we turn warnings into errors.
-// VMOptions=--fatal-type-errors --enable_type_errors
+// VMOptions=--enable_type_errors
 
 #library("Prefix22NegativeTest.dart");
 #import("library12.dart", prefix:"lib12");
 
 class myClass {
-  lib12.Library13 fld; // static type warning
+  lib12.Library13 fld; /// static type error
 }
 
 main() {