[clang] [CodeGen] Apply 'readonly' to 'this' pointer argument. (PR #106499)

[Nikita Popov via cfe-commits]

https://github.com/nikic requested changes to this pull request.

I'm very confused. `readonly` means that the memory behind `this` cannot be changed, not that the pointer cannot be changed.

https://github.com/llvm/llvm-project/pull/106499