[compiler-rt] [PAC][compiler-rt] Fix init/fini array signing schema (PR #150691)

[Anatoly Trosinenko via llvm-commits]

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

I'm not sure whether fixing clang-format violations is strictly required in the `builtins` library (by the way, even in this file I can see an indented `define`, though only a single line), but in other respects this patch looks good to me.

> When `ptrauth_calls` is present but `ptrauth_init_fini` is not, compiler emits raw unsigned pointers in `.init_array`/`.fini_array` sections. Previously, `__do_init`/`__do_fini` pointers in these sections were implicitly signed (due to the presense of `ptrauth_calls`).

Considering the description, it feels like it could be made a bit easier to understand by mentioning that `__do_init` and `__do_fini` pointers are **explicitly** added to these sections - that's why they ended up being implicitly signed while every other pointer was non-signed.

https://github.com/llvm/llvm-project/pull/150691