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

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

@DavidSpickett Thank you for the comments! I will rebase the branch as-is to a recent version of `main` to retest it before merging.

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