[flags] Prepare contradictory-flags warning

Bug: v8:10577
Change-Id: Ia546984711fa47978dafa139cce7a0388ef5c347
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2416369
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69970}

src/flags/flag-definitions.h

@@ -203,6 +203,13 @@ struct MaybeBoolFlag {
 //
 #define FLAG FLAG_FULL
 
+// TODO(tebbi): This is a dummy atm to prepare the infra call sites.
+DEFINE_BOOL(abort_on_contradictory_flags, false,
+            "Disallow flags or implications overriding each other.")
+// This implication is also hard-coded into the flags processing to make sure it
+// becomes active before we even process subsequent flags.
+DEFINE_NEG_IMPLICATION(fuzzing, abort_on_contradictory_flags)
+
 // Flags for language modes and experimental language features.
 DEFINE_BOOL(use_strict, false, "enforce strict mode")
 

tools/testrunner/num_fuzzer.py

@@ -117,6 +117,10 @@ class NumFuzzer(base_runner.BaseTestRunner):
   def _get_default_suite_names(self):
     return DEFAULT_SUITES
 
+  def _runner_flags(self):
+    """Extra default flags specific to the test runner implementation."""
+    return ['--no-abort-on-contradictory-flags']
+
   def _get_statusfile_variables(self, options):
     variables = (
         super(NumFuzzer, self)._get_statusfile_variables(options))