This is a reland of 2000aea5
Changes compared to last reland:
- Add rule in variants.py for --enable_experimental_regexp_engine.
- Make sure --abort-on-contradictory-flags works as well as --fuzzing
  to disable the checking for fuzzers, including for d8 flags.

Original change's description:
> Reland^4 "[flags] warn about contradictory flags"
>
> This is a reland of 0ba115e6
> Changes compared to last reland:
> - Fix Python code trying to write to expected_outcomes, which is now a
>   computed property.
> - Fix remaining place in d8.cc that ignored the --fuzzing flag.
> - Expect flag contradictions for --cache in code_serializer variant.
>
> Original change's description:
> > Reland^3 "[flags] warn about contradictory flags"
> >
> > Changes:
> > - Also allow second parameter influenced by --cache to be reassigned.
> > - Fix --stress-opt to only --always-opt in the last iteration as before.
> >
> > Original change's description:
> > > Reland^2 "[flags] warn about contradictory flags"
> > >
> > > This is a reland of d8f8a7e2
> > > Change compared to last reland:
> > > - Do not check for d8 flag contradictions in the presence of --fuzzing
> > > - Allow identical re-declaration of --cache=*
> > >
> > > Original change's description:
> > > > Reland "[flags] warn about contradictory flags"
> > > >
> > > > This is a reland of b8f91666
> > > > Difference to previous CL: Additional functionality to specify
> > > > incompatible flags based on GN variables and extra-flags, used
> > > > to fix the issues that came up on the waterfall.
> > > >
> > > > This also changes the rules regarding repeated flags: While
> > > > explicitly repeated flags are allowed for boolean values as long
> > > > as they are identical, repeated flags or explicit flags in the
> > > > presence of an active implication are disallowed for non-boolean
> > > > flags. The latter simplifies specifying conflict rules in
> > > > variants.py. Otherwise a rule like
> > > >
> > > > INCOMPATIBLE_FLAGS_PER_EXTRA_FLAG = {
> > > >   "--gc-interval=*": ["--gc-interval=*"],
> > > > }
> > > >
> > > > wouldn't work because specifying the same GC interval twice
> > > > wouldn't actually count as a conflict. This was an issue with
> > > > test/mjsunit/wasm/gc-buffer.js, which specifies
> > > > --gc-interval=500 exactly like the extra flag by the stress bot.
> > > >
> > > > Also, this now expands contradictory flags checking to d8 flags
> > > > for consistency.
> > > >
> > > > Original change's description:
> > > > > [flags] warn about contradictory flags
> > > > >
> > > > > Design Doc: https://docs.google.com/document/d/1lkvu8crkK7Ei39qjkPCFijpNyxWXsOktG9GB-7K34jM/
> > > > >
> > > > > Bug: v8:10577
> > > > > Change-Id: Ib9cfdffa401c48c895bf31caed5ee03545beddab
> > > > > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2154792
> > > > > Reviewed-by: Clemens Backes <clemensb@chromium.org>
> > > > > Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> > > > > Reviewed-by: Georg Neis <neis@chromium.org>
> > > > > Reviewed-by: Tamer Tas <tmrts@chromium.org>
> > > > > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> > > > > Cr-Commit-Position: refs/heads/master@{#68168}
> > > >
> > > > Bug: v8:10577
> > > > Change-Id: I268e590ee18a535b13dee14eeb15ddd0a9ee8341
> > > > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2235115
> > > > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> > > > Reviewed-by: Tamer Tas <tmrts@chromium.org>
> > > > Reviewed-by: Clemens Backes <clemensb@chromium.org>
> > > > Reviewed-by: Georg Neis <neis@chromium.org>
> > > > Cr-Commit-Position: refs/heads/master@{#68989}
> > >
> > > Bug: v8:10577
> > > Change-Id: I31d2794d4f9ff630f3444210100c64d67d881276
> > > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2339464
> > > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> > > Reviewed-by: Clemens Backes <clemensb@chromium.org>
> > > Cr-Commit-Position: refs/heads/master@{#69339}
> >
> > Bug: v8:10577
> > Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng
> > Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
> > Change-Id: I4a69dc57a102782cb453144323e3752ac8278624
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2352770
> > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> > Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> > Reviewed-by: Clemens Backes <clemensb@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#69433}
>
> Change-Id: Ib6d2aeb495210f581ac671221c265df58e8e5e70
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2398640
> Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Tamer Tas <tmrts@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#69954}

Bug: v8:10577
TBR: clemensb@chromium.org, tmrts@chromium.org
Change-Id: Iab2d32cdcc2648934fc52255ccf3ae3ec9ca4d9b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2416386Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70000}