[llvm] [clang] [AArch64] Make Armv8.3-a extension set +pauth by default (PR #78027)

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

No-change rebase to fix the merge conflict. This time shown as a single commit, as expected. I do understand that LLVM review policy suggests to only rebase right before "squash and merge", but there are no comments yet and the conflict is almost as large as the patch itself :)

https://github.com/llvm/llvm-project/pull/78027