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

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

Fixed the tests in 85c21ecb922826ae8fabb4bc0c518933f19e0634:
* do not add attributes on the call site (something was probably wrong with the way I was running the tests, as this should fail before the rebase as well...)
* added `setPointerAuthFnAttributes` as a counterpart of `setBranchProtectionFnAttributes` (in [clang/test/CodeGenCXX/ptrauth.cpp](https://github.com/llvm/llvm-project/blob/00c5cd8a7a3f7e363d8f0d172ea88af91612c7fa/clang/test/CodeGenCXX/ptrauth.cpp#L21) `std::terminate()` is implemented, but by the time its implementation is emitted, `GetOrCreateLLVMFunction` was already called without a `Decl`, thus lazy-initializing a function, but without the attributes)

> I may start working on moving the preferences into the targetinfo unless you're working on that already

@ojhunt I'm not working on it, thank you!

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