Introduce --fuzzing flag

This is still unused but will eventually be used by fuzzers.

Bug: v8:10249
Change-Id: Ib592a5a8da1399ad8fb5a277ea94fda68b382058
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2141735Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67059}

src/flags/flag-definitions.h

@@ -1361,9 +1361,14 @@ DEFINE_INT(testing_prng_seed, 42, "Seed used for threading test randomness")
 // Test flag for a check in %OptimizeFunctionOnNextCall
 DEFINE_BOOL(
     testing_d8_test_runner, false,
-    "test runner turns on this flag to enable a check that the funciton was "
+    "test runner turns on this flag to enable a check that the function was "
     "prepared for optimization before marking it for optimization")
 
+DEFINE_BOOL(
+    fuzzing, false,
+    "Fuzzers use this flag to signal that they are ... fuzzing. This causes "
+    "intrinsics to fail silently (e.g. return undefined) on invalid usage.")
+
 // mksnapshot.cc
 DEFINE_STRING(embedded_src, nullptr,
               "Path for the generated embedded data file. (mksnapshot only)")