[test] ReturnFuzzSafe only returns undefined when correctness fuzzing

Change ReturnFuzzSafe to only return undefined when
--correctness-fuzzer-supressions is on, instead of --fuzzing.

Bug: chromium:1200724, v8:11701
Change-Id: I21aa77db89fe26308881985055b023a5c03c2518
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2905593
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Auto-Submit: Patrick Thier <pthier@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74671}

src/runtime/runtime-test.cc

@@ -42,9 +42,12 @@ V8_WARN_UNUSED_RESULT Object CrashUnlessFuzzing(Isolate* isolate) {
   return ReadOnlyRoots(isolate).undefined_value();
 }
 
-// Returns |value| unless fuzzing is enabled, otherwise returns undefined_value.
+// Returns |value| unless correctness-fuzzer-supressions is enabled,
+// otherwise returns undefined_value.
 V8_WARN_UNUSED_RESULT Object ReturnFuzzSafe(Object value, Isolate* isolate) {
-  return FLAG_fuzzing ? ReadOnlyRoots(isolate).undefined_value() : value;
+  return FLAG_correctness_fuzzer_suppressions
+             ? ReadOnlyRoots(isolate).undefined_value()
+             : value;
 }
 
 // Assert that the given argument is a number within the Int32 range