This is a reland of f23f644f

Fix the issue by wrap v8_executable("gen-regexp-special-case")
inside if (current_toolchain == v8_generator_toolchain) {
and change deps of action("run_gen-regexp-special-case")
to  ":gen-regexp-special-case($v8_generator_toolchain)",


Original change's description:
> Speed up CharacterRange::AddCaseEquivalents
>
> By using the lexCss("color:") to measure the performance
> The change make the lexCss("color:")
>   x21 - x40 times faster than trunk.
>   x2.3 - x4.6 times faster than m74.
>
> Design Doc: http://shorturl.at/adfO5
>
> Measured by out/x64.release/d8 reg977003.js
> see reg977003.js attached to chromium:977003
>
> Also see another cl of benchmark in
> https://chromium-review.googlesource.com/c/v8/v8/+/1679651/
>
>
> Bug: chromium:977003
> Change-Id: Ie8518493d2c33df1594be1b4576bda715087b421
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1674851
> Commit-Queue: Frank Tang <ftang@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#62471}

Bug: chromium:977003
Change-Id: Ie690810f596e9551b5765f422665c9617391bcf8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1683706Reviewed-by: Frank Tang <ftang@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62486}