[flags] Avoid endless lops when enforcing flag implications

Change-Id: Ide8935a02cb64134c3bdeb8b3e38e9a6e043e13c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3610432Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80256}

src/flags/flags.cc

@@ -841,11 +841,15 @@ bool TriggerImplication(bool premise, const char* premise_name,
 void FlagList::EnforceFlagImplications() {
   flag_hash = 0;
   bool changed;
+  int iteration = 0;
   do {
     changed = false;
 #define FLAG_MODE_DEFINE_IMPLICATIONS
 #include "src/flags/flag-definitions.h"  // NOLINT(build/include)
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
+    // Make sure flag definitions are not touring complete. A.k.a  avoid endless
+    // loops in case of buggy configurations.
+    CHECK_LT(iteration++, 1000);
   } while (changed);
 }