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

[Daniel Kiss via cfe-commits]

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

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

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