[clang] [clang][AArch64] Move initialization of ptrauth-* function attrs (PR #140277)

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

It seems that when I rebased this PR from an older version of `main` branch, some test failures came up. I'm investigating these now. An example is [clang/test/CodeGen/ptrauth-function-lvalue-cast.c](https://github.com/llvm/llvm-project/blob/00c5cd8a7a3f7e363d8f0d172ea88af91612c7fa/clang/test/CodeGen/ptrauth-function-lvalue-cast.c#L12), where an attribute was added at call site:
```llvm
  call void %0() #1 [ "ptrauth"(i32 0, i64 0) ]
;                ^^
```

> maybe worth to review the attribute handling for the synthetic function's attributes in llvm too.

@DanielKristofKiss As far as I know, at least one example of synthetic functions not protected with pac-ret is Function Multi Versioning resolvers. This could be fixed via a separate PR, though.


https://github.com/llvm/llvm-project/pull/140277