[llvm] Use exec_script_allowlist in //llvm/utils/gn/.gn (PR #134172)

[Nico Weber via llvm-commits]

https://github.com/nico approved this pull request.

lg, but please give me a bit to update the bots.

Do you want to update the comment right above too?

Could you also update https://github.com/llvm/llvm-project/blob/783201b184572a07efe2dc6b6b9110873421cf11/llvm/utils/gn/build/toolchain/BUILD.gn#L86 ? (Move it to top of file; update comment.)

Another idea could be to assign to one or the other depending on `gn_version`.

But I think fairly few people use this build, and it's fairly easy to update GN (just run `llvm/utils/gn/get.py`), so I think it's fine to just require a new(ish) version of GN.

https://github.com/llvm/llvm-project/pull/134172